Fixes a number of crashes:
- Fixes a crash when trying to reuse previously saved export settings which refer to a saved connection that no longer exists.
- Fixes a crash which could occur when filtering the saved queries list and the selected saved query is removed.
- Fixes a crash when clicking to edit an unloaded value in the vertical editor, when the pk of that row is stale so the load fails.
- No longer crashes when opening a table/view in an SQLite database "Open in New Tab".
- Fixes crashes which could occur when filtering the primary (left) sidebar.
- Fixes a crash in the Query view when typing SQL when connected to an SQLite database.
- Fixes a crash in the Query view when exporting results from a SELECT query that had certain SQL expressions as column names.