bugfix: avoid bug if domSelection is not displayed in the webpage

[NomadeLampe]

Hello, during my work I use Kendo Editor which use this component. It appear that from time to time on Chrome we have the following error TypeError: Cannot read properties of null (reading 'focusNode')\n at EditorView.updateStateInner.

I believe that this small change would prevent this bug.

[marijnh]

According to the spec Document.getSelection (which is where this value originates) should always return a Selection object unless the document has no browsing context (isn't any window's actual active document). If that is a thing that actually happens in the wild, we'll need to adjust more than just this to account for it. Do you have a way to reproduce this crash or more information about what might be going on when it happens?

[NomadeLampe]

I have notice this typing from typescript where it return Selection | null but in index.ts the typing looks wrong.

Regarding the way to reproduce it, I will try but I can't copy any code. It happen when use multiple instance of kendo-editor and try to interact with the first one while having a pop-in hiding the editor.