[#320] prevent possible NPE in isFileOpenedInLspEditor

[ghentschke]

getEditor can return null.

may be a fix for #320

[jonahgraham]

I am going to contribute the build that contains this change as the contribution to 2024-06 M3 - this will allow consumers to test it as part of the IDE later this week more easily

[ghentschke]

Yes, that's a good idea!