Description:
On Fedora 31 with AlternateTab Gnome Shell Extension enabled, when I am switching between LibreOffice Draw and Calc using "Alt+Tab" key combination, the application crashes.

Steps to Reproduce:
1. Enable AlternateTab Gnome Shell extension. 
(https://extensions.gnome.org/extension/15/alternatetab/)
2. New Draw, then New Calc.
3. Switch back to the draw document, hit F2 and type "test". Do not click anywhere at this moment.
4. Alt+Tab to switch to the Calc document, then Alt+Tab again back to the Draw document.

--> Crashes in step 4.

I don't believe the AlternateTab here is causing the problem. This Gnome Shell extension is here just for the purpose to let the windows do not group by application (this is because in the current Gnome, windows are grouped by application, so by default if you switch between windows using Alt+Tab, you switch to another application rather than from Draw to Calc in this case). As a result.

Type in "test" in Draw then using your mouse-click to switch to Calc does not trigger this crash.

At the time of crash, the following SAL messages:
> warn:vcl.gdi:18629:18629:vcl/source/bitmap/bitmapfilter.cxx:26: Bitmap filter failed
> warn:vcl.gdi:18629:18629:vcl/source/bitmap/bitmapfilter.cxx:26: Bitmap filter failed
> warn:vcl:18629:18629:vcl/source/window/winproc.cxx:858: ImplHandleKey: Keyboard-Input is sent to a frame without focus
> warn:vcl:18629:18629:vcl/source/window/winproc.cxx:858: ImplHandleKey: Keyboard-Input is sent to a frame without focus
> warn:legacy.osl:18629:18629:sfx2/source/sidebar/DeckLayouter.cxx:543: OSL_ASSERT: nRemainingHeightToDistribute==0
> warn:legacy.osl:18629:18629:svx/source/svdraw/svdmrkv1.cxx:314: SdrMarkView::UndirtyMrkPnt(): Selected points on an object that is not a PolyObj!
> 
> (soffice:18629): GLib-GObject-CRITICAL **: 17:02:20.765: g_object_get_qdata: assertion 'G_IS_OBJECT (object)' failed

Actual Results:
Crashes in step 4.

Expected Results:
LibreOffice should never crash.
LibreOffice should never crash even through there is a bug in Gnome or Gnome Sheel Extension itself!


Reproducible: Always


User Profile Reset: No



Additional Info:
Version: 7.0.0.0.alpha0+
Build ID: a092262a573d185171b00d2848cc25c14ad33b6e
CPU-thread: 4; OS: Linux 5.4; UI-render: Default; VCL: gtk3; 
Locale: zh-CN (zh_CN.UTF-8); UI Language: zh-CN
Calc: threaded


Also in the following version on the same computer:
6.3.6.0.0+, Build ID: cb957e35f54d6c4e9b8b13cd014a09bdf74327b0