Fix crash on delete in Selectors and CSS dialog (windows)
Fix crash deleting row, Selectors dialog on Windows
_deletion doesn't seem necessary (only used in one place). I've removed that use, replacing it with a defensive check to avoid crashing, though we might end up selecting a different cell now. Now _deletion is only true during the call to _onPropDelete, and is used to stop readStyleElement from running and deleting the tree view, which is still used by a caller of _onPropDelete (gtk_tree_view_multipress_gesture_pressed).
The "selecting a different cell" I mention in the commit above only occurs if you delete the current row in the 50 ms (possibly longer due to lag) after you hit finish editing the left-most cell.
Still untested, but this approach seems more logical.
Old approach:
Similar fix to 1d5f25f2
Haven't tested to see if it works, though it compiles. Oops, sorry for resetting pipelines midway, had a brainfart.