WebGLVertexArrayObjectOES's destructor shouldn't send infallible webgl commands

[jdm]

I got this when closing https://servo.org/hl-home/bbjs/#8Y780Y#57:

called `Result::unwrap()` on an `Err` value: () (thread ScriptThread PipelineId { namespace_id: PipelineNamespaceId(1), index: PipelineIndex(1) }, at components/script/dom/webglrenderingcontext.rs:360)
stack backtrace:
   0: backtrace::backtrace::trace_unsynchronized
   1: <servo::backtrace::Print as core::fmt::Debug>::fmt
   2: core::fmt::write
   3: std::io::Write::write_fmt
   4: servo::backtrace::print
   5: servo::main::{{closure}}
   6: std::panicking::rust_panic_with_hook
   7: rust_begin_unwind
   8: core::panicking::panic_fmt
   9: core::option::expect_none_failed
  10: core::result::Result<T,E>::unwrap
  11: script::dom::webglrenderingcontext::WebGLRenderingContext::send_command
  12: script::dom::webglbuffer::WebGLBuffer::delete
  13: script::dom::webglbuffer::WebGLBuffer::decrement_attached_counter
  14: script::dom::webglvertexarrayobjectoes::WebGLVertexArrayObjectOES::delete
  15: <script::dom::webglvertexarrayobjectoes::WebGLVertexArrayObjectOES as core::ops::drop::Drop>::drop
  16: core::ptr::drop_in_place
  17: core::ptr::drop_in_place
  18: script::dom::bindings::codegen::Bindings::WebGLVertexArrayObjectOESBinding::WebGLVertexArrayObjectOESBinding::_finalize::{{closure}}
  19: core::ops::function::FnOnce::call_once
  20: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
  21: std::panicking::try::do_call
  22: __rust_maybe_catch_panic
  23: std::panicking::try
  24: std::panic::catch_unwind
  25: mozjs::panic::wrap_panic
  26: script::dom::bindings::codegen::Bindings::WebGLVertexArrayObjectOESBinding::WebGLVertexArrayObjectOESBinding::_finalize
  27: _ZN2js2gc5Arena8finalizeI8JSObjectEEmPNS_6FreeOpENS0_9AllocKindEm
  28: _ZL19FinalizeTypedArenasI8JSObjectEbPN2js6FreeOpEPPNS1_2gc5ArenaERNS4_15SortedArenaListENS4_9AllocKindERNS1_11SliceBudgetENS4_10ArenaLists14KeepArenasEnumE
  29: _ZN2js2gc10ArenaLists18foregroundFinalizeEPNS_6FreeOpENS0_9AllocKindERNS_11SliceBudgetERNS0_15SortedArenaListE
  30: _ZN2js2gc9GCRuntime17finalizeAllocKindEPNS_6FreeOpERNS_11SliceBudgetEPN2JS4ZoneENS0_9AllocKindE
  31: _ZN11sweepaction18SweepActionForEachI13ContainerIterIN7mozilla7EnumSetIN2js2gc9AllocKindEjEEES7_JPNS5_9GCRuntimeEPNS4_6FreeOpERNS4_11SliceBudgetEPN2JS4ZoneEEE3runESA_SC_SE_SH_
  32: _ZN11sweepaction19SweepActionSequenceIJPN2js2gc9GCRuntimeEPNS1_6FreeOpERNS1_11SliceBudgetEPN2JS4ZoneEEE3runES4_S6_S8_SB_
  33: _ZN11sweepaction18SweepActionForEachIN2js2gc19SweepGroupZonesIterEP9JSRuntimeJPNS2_9GCRuntimeEPNS1_6FreeOpERNS1_11SliceBudgetEEE3runES7_S9_SB_
  34: _ZN11sweepaction19SweepActionSequenceIJPN2js2gc9GCRuntimeEPNS1_6FreeOpERNS1_11SliceBudgetEEE3runES4_S6_S8_
  35: _ZN11sweepaction20SweepActionRepeatForIN2js2gc15SweepGroupsIterEP9JSRuntimeJPNS2_9GCRuntimeEPNS1_6FreeOpERNS1_11SliceBudgetEEE3runES7_S9_SB_
  36: _ZN2js2gc9GCRuntime19performSweepActionsERNS_11SliceBudgetE
  37: _ZN2js2gc9GCRuntime16incrementalSliceERNS_11SliceBudgetEN2JS8GCReasonERNS0_13AutoGCSessionE
  38: _ZN2js2gc9GCRuntime7gcCycleEbNS_11SliceBudgetEN2JS8GCReasonE
  39: _ZN2js2gc9GCRuntime7collectEbNS_11SliceBudgetEN2JS8GCReasonE
  40: _ZN2js2gc9GCRuntime2gcE18JSGCInvocationKindN2JS8GCReasonE
  41: _ZN9JSRuntime14destroyRuntimeEv
  42: _ZN2js14DestroyContextEP9JSContext
  43: <mozjs::rust::Runtime as core::ops::drop::Drop>::drop
  44: core::ptr::drop_in_place
  45: core::ptr::drop_in_place
  46: core::ptr::drop_in_place
  47: <alloc::rc::Rc<T> as core::ops::drop::Drop>::drop
  48: core::ptr::drop_in_place
  49: core::ptr::drop_in_place
  50: <script::script_thread::ScriptThread as script_traits::ScriptThreadFactory>::create::{{closure}}
  51: std::sys_common::backtrace::__rust_begin_short_backtrace
  52: std::thread::Builder::spawn_unchecked::{{closure}}::{{closure}}
  53: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
  54: std::panicking::try::do_call
  55: __rust_maybe_catch_panic
  56: std::panicking::try
  57: std::panic::catch_unwind
  58: std::thread::Builder::spawn_unchecked::{{closure}}
  59: core::ops::function::FnOnce::call_once{{vtable.shim}}
  60: <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once
  61: std::sys::unix::thread::Thread::new::thread_start
  62: _pthread_start