fix RSOD when deleting a tiddler

This PR should fix - #457 - Related [Talk thread](https://talk.tiddlywiki.org/t/please-help-final-checks-for-bug-fix-release-v5-3-5/10104/9?u=pmario) As I wrote it does fix the RSOD it for me, but I'm not 100% sure if all the functionality works as expected.