Fix error "couldn't get FX param value"

[helgoboss]

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Module name:         ReaLearn
Module version:      v1.12.0-pre12/x86_64 rev de942f (2021-01-20 14:50:42 UTC)
Module base address: 0x7ff823b20000
Module size:         0xb27000

Message: couldn't get FX param value: ReaperFunctionError { message: "couldn\'t get current FX parameter value (probably FX or parameter doesn\'t exist)" }

   0:     0x7ff8241f503d - backtrace::backtrace::dbghelp::trace
                               at C:\Users\runneradmin\.cargo\registry\src\github.com-1ecc6299db9ec823\backtrace-0.3.53\src\backtrace\dbghelp.rs:108
   1:     0x7ff8241f503d - backtrace::backtrace::trace_unsynchronized
                               at C:\Users\runneradmin\.cargo\registry\src\github.com-1ecc6299db9ec823\backtrace-0.3.53\src\backtrace\mod.rs:66
   2:     0x7ff8241f503d - backtrace::backtrace::trace<closure-0>
                               at C:\Users\runneradmin\.cargo\registry\src\github.com-1ecc6299db9ec823\backtrace-0.3.53\src\backtrace\mod.rs:53
   3:     0x7ff8241f3559 - backtrace::capture::Backtrace::create
                               at C:\Users\runneradmin\.cargo\registry\src\github.com-1ecc6299db9ec823\backtrace-0.3.53\src\capture.rs:176
   4:     0x7ff8241f3559 - backtrace::capture::Backtrace::new
                               at C:\Users\runneradmin\.cargo\registry\src\github.com-1ecc6299db9ec823\backtrace-0.3.53\src\capture.rs:140
   5:     0x7ff8241130ff - reaper_high::log_util::create_reaper_panic_hook::{{closure}}<closure-0>
                               at C:\Users\runneradmin\.cargo\git\checkouts\reaper-rs-d32fed07113e6874\1b06a2f\main\high\src\log_util.rs:51
   6:     0x7ff824211b30 - std::panicking::rust_panic_with_hook
                               at /rustc/f0f68778f798d6d34649745b41770829b17ba5b8\/library\std\src\panicking.rs:595
   7:     0x7ff824211601 - std::panicking::begin_panic_handler::{{closure}}
                               at /rustc/f0f68778f798d6d34649745b41770829b17ba5b8\/library\std\src\panicking.rs:497
   8:     0x7ff82420e9bf - std::sys_common::backtrace::__rust_end_short_backtrace<closure-0,!>
                               at /rustc/f0f68778f798d6d34649745b41770829b17ba5b8\/library\std\src\sys_common\backtrace.rs:141
   9:     0x7ff824211559 - std::panicking::begin_panic_handler
                               at /rustc/f0f68778f798d6d34649745b41770829b17ba5b8\/library\std\src\panicking.rs:493
  10:     0x7ff824224ab0 - core::panicking::panic_fmt
                               at /rustc/f0f68778f798d6d34649745b41770829b17ba5b8\/library\core\src\panicking.rs:92
  11:     0x7ff824224913 - core::option::expect_none_failed
                               at /rustc/f0f68778f798d6d34649745b41770829b17ba5b8\/library\core\src\option.rs:1268
  12:     0x7ff823ee1d01 - core::result::Result<reaper_medium::misc_newtypes::ReaperNormalizedFxParamValue, reaper_medium::errors::ReaperFunctionError>::expect
                               at /rustc/f0f68778f798d6d34649745b41770829b17ba5b8\library\core\src\result.rs:933
  13:     0x7ff823ee1d01 - realearn::domain::reaper_target::{{impl}}::current_value
                               at D:\a\realearn\realearn\main\src\domain\reaper_target.rs:948
  14:     0x7ff823c3f16c - realearn::domain::mapping::MainMapping::feedback_if_enabled
                               at D:\a\realearn\realearn\main\src\domain\mapping.rs:253
  15:     0x7ff823da2be1 - realearn::domain::main_processor::{{impl}}::run::{{closure}}
                               at D:\a\realearn\realearn\main\src\domain\main_processor.rs:423
  16:     0x7ff823da2be1 - core::ops::function::impls::{{impl}}::call_mut
                               at /rustc/f0f68778f798d6d34649745b41770829b17ba5b8\library\core\src\ops\function.rs:269
  17:     0x7ff823da2be1 - core::iter::traits::iterator::Iterator::find_map::check::{{closure}}
                               at /rustc/f0f68778f798d6d34649745b41770829b17ba5b8\library\core\src\iter\traits\iterator.rs:2257
  18:     0x7ff823da2be1 - core::iter::traits::iterator::Iterator::try_fold
                               at /rustc/f0f68778f798d6d34649745b41770829b17ba5b8\library\core\src\iter\traits\iterator.rs:1888
  19:     0x7ff823da2be1 - core::iter::traits::iterator::Iterator::find_map
                               at /rustc/f0f68778f798d6d34649745b41770829b17ba5b8\library\core\src\iter\traits\iterator.rs:2263
  20:     0x7ff823da2be1 - core::iter::adapters::filter_map::{{impl}}::next
                               at /rustc/f0f68778f798d6d34649745b41770829b17ba5b8\library\core\src\iter\adapters\filter_map.rs:61
  21:     0x7ff823da2be1 - realearn::domain::main_processor::MainProcessor<alloc::rc::Weak<core::cell::RefCell<realearn::application::session::Session>>>::send_feedback
                               at D:\a\realearn\realearn\main\src\domain\main_processor.rs:465
  22:     0x7ff823da2be1 - realearn::domain::main_processor::MainProcessor<alloc::rc::Weak<core::cell::RefCell<realearn::application::session::Session>>>::run<alloc::rc::Weak<core::cell::RefCell<realearn::application::session::Session>>>
                               at D:\a\realearn\realearn\main\src\domain\main_processor.rs:425
  23:     0x7ff823ede13c - realearn::domain::control_surface::RealearnControlSurfaceMiddleware<alloc::rc::Weak<core::cell::RefCell<realearn::application::session::Session>>>::run_internal<alloc::rc::Weak<core::cell::RefCell<realearn::application::session::Session>>>
                               at D:\a\realearn\realearn\main\src\domain\control_surface.rs:109
  24:     0x7ff8241485ef - reaper_low::control_surface::Run::{{closure}}
                               at C:\Users\runneradmin\.cargo\git\checkouts\reaper-rs-d32fed07113e6874\1b06a2f\main\low\src\control_surface.rs:219
  25:     0x7ff8241485ef - std::panic::{{impl}}::call_once
                               at /rustc/f0f68778f798d6d34649745b41770829b17ba5b8\library\std\src\panic.rs:322
  26:     0x7ff8241485ef - std::panicking::try::do_call
                               at /rustc/f0f68778f798d6d34649745b41770829b17ba5b8\library\std\src\panicking.rs:379
  27:     0x7ff8241485ef - std::panicking::try
                               at /rustc/f0f68778f798d6d34649745b41770829b17ba5b8\library\std\src\panicking.rs:343
  28:     0x7ff8241485ef - std::panic::catch_unwind
                               at /rustc/f0f68778f798d6d34649745b41770829b17ba5b8\library\std\src\panic.rs:396
  29:     0x7ff8241485ef - reaper_low::util::firewall
                               at C:\Users\runneradmin\.cargo\git\checkouts\reaper-rs-d32fed07113e6874\1b06a2f\main\low\src\util.rs:18
  30:     0x7ff8241485ef - reaper_low::control_surface::Run
                               at C:\Users\runneradmin\.cargo\git\checkouts\reaper-rs-d32fed07113e6874\1b06a2f\main\low\src\control_surface.rs:219
  31:        0x140271888 - <unknown>
  32:        0x140191cab - <unknown>
  33:        0x140190ed4 - <unknown>
  34:        0x1403ac865 - <unknown>
  35:     0x7ff882b02920 - ScreenToClient
  36:     0x7ff882b020c2 - ScreenToClient
  37:     0x7ff882b49f99 - UnpackDDElParam
  38:     0x7ff882afe858 - CallWindowProcW
  39:     0x7ff882afe299 - DispatchMessageW
  40:        0x1403a60e1 - <unknown>
  41:        0x1408757a1 - <unknown>
  42:     0x7ff883c57034 - BaseThreadInitThunk
  43:     0x7ff883f5d241 - RtlUserThreadStart
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