assertion failed: count_cell.get() > 0

[gerdneuman]

Got this when trying today's nightly on Linux (Ubuntu 16-04) with the below website:

assertion failed: count_cell.get() > 0

URL:

https://berlin.fau.org/

Backtrace:

frame #0  - 0x000055cb4aa0cd8d - backtrace::backtrace::trace::hccde8df28b4db2a2
frame #1  - 0x000055cb4aa0cd15 - backtrace::capture::Backtrace::new::h42f95930bb8c5ee8
frame #2  - 0x000055cb49bda359 - _<F as alloc..boxed..FnBox<A>>::call_box::hc555946005547ceb
frame #3  - 0x000055cb4aa03b98 - util::panicking::initiate_panic_hook::_$u7b$$u7b$closure$u7d$$u7d$::_$u7b$$u7b$closure$u7d$$u7d$::hc61828c8a9f6df01
frame #4  - 0x000055cb4ab0b14c - std::panicking::rust_panic_with_hook::h983af77c1a2e581b
frame #5  - 0x000055cb4941cedf - std::panicking::begin_panic::h0bf39f6d43ab9349
frame #6  - 0x000055cb49a8f490 - _<script..dom..htmllinkelement..StylesheetContext as net_traits..AsyncResponseListener>::response_complete::h71d7672a3472afa1
frame #7  - 0x000055cb49a8cf9b - _<script..network_listener..ListenerRunnable<A, Listener> as script..script_thread..Runnable>::handler::h724ec798d0dfe84e
frame #8  - 0x000055cb49be52a4 - script::script_thread::ScriptThread::handle_msg_from_script::hfac8a5d67415fa31
frame #9  - 0x000055cb49c368ef - script::script_thread::ScriptThread::handle_msgs::_$u7b$$u7b$closure$u7d$$u7d$::hcc3e5fcf08d42e0c
frame #10 - 0x000055cb49c1dad7 - script::script_thread::ScriptThread::handle_msgs::hf9fbf9949e23273b
frame #11 - 0x000055cb49bd8a47 - std::panicking::try::call::h99112171a9854ab3
frame #12 - 0x000055cb4ab2f95b - __rust_try
frame #13 - 0x000055cb4ab2f8fe - __rust_maybe_catch_panic
frame #14 - 0x000055cb49bd9cbd - _<F as alloc..boxed..FnBox<A>>::call_box::h4410a344b31b72da
frame #15 - 0x000055cb4ab23924 - std::sys::thread::Thread::new::thread_start::h9c883b6d445ece46
frame #16 - 0x00007f31347fa6f9 - start_thread
frame #17 - 0x00007f313431ab5c - clone
frame #18 - 0x0000000000000000 - <unknown>

[nox]

Thanks for the report! Closing as a duplicate of #12047.