KWin sometimes crashes when leaving the "Present windows" screen.

Occasionally, the crash can be triggered by:

1. setting the top left corner as a hot corner for "present windows"
2. move the mouse cursor to the top left corner (which should trigger "present windows" now) and click multiple times without moving the cursor

Support information: https://paste.xinu.at/nwQ7Y/

I've tried to build kwin with the following flags:

export CFLAGS="-Og -ggdb3 -fvar-tracking-assignments"
export CXXFLAGS="-Og -ggdb3 -fvar-tracking-assignments"

but the stack trace still does not seem very useful:

(gdb) bt
#0  0x00007f901745d355 in raise () at /usr/lib/libc.so.6
#1  0x00007f9018d03290 in KCrash::defaultCrashHandler(int) () at /usr/lib/libKF5Crash.so.5
#2  0x00007f901745d3e0 in <signal handler called> () at /usr/lib/libc.so.6
#3  0x000055f03fbfae00 in  ()
#4  0x00007f9018e833ff in KWin::Workspace::workspaceEvent(xcb_generic_event_t*) (this=0x55f03ee683f0, e=e@entry=0x7f900c0133f0) at /usr/include/c++/10.1.0/bits/atomic_base.h:325
#5  0x00007f9018ebd845 in KWin::XcbEventFilter::nativeEventFilter(QByteArray const&, void*, long*) (this=<optimized out>, eventType=..., message=0x7f900c0133f0, result=<optimized out>)
    at /build/kwin/src/kwin-5.18.90/workspace.h:76
#6  0x00007f9017aa0b47 in QAbstractEventDispatcher::filterNativeEvent(QByteArray const&, void*, long*) () at /usr/lib/libQt5Core.so.5
#7  0x00007f9011703703 in QXcbConnection::handleXcbEvent(xcb_generic_event_t*) () at /usr/lib/libQt5XcbQpa.so.5
#8  0x00007f9011704c79 in QXcbConnection::processXcbEvents(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/libQt5XcbQpa.so.5
#9  0x00007f901172806e in  () at /usr/lib/libQt5XcbQpa.so.5
#10 0x00007f9017aa201c in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () at /usr/lib/libQt5Core.so.5
#11 0x00007f9017aaa4a4 in QCoreApplication::exec() () at /usr/lib/libQt5Core.so.5
#12 0x000055f03dba20ef in main(int, char**) (argc=<optimized out>, argv=0x7fffd2026968) at /build/kwin/src/kwin-5.18.90/main_x11.cpp:479


Operating System: Arch Linux 
KDE Plasma Version: 5.18.90
KDE Frameworks Version: 5.70.0
Qt Version: 5.15.0