Blender Git Loki

Fix T49199: Combination of dialog + wm.open_mainfile causes crash

Issue was that the wm.open_mainfile OP caused all handlers to be removed and since rB45592291 cancelled (which is correct in general), the menu that triggered the OP should not be cancelled though.
Not sure if this is a nice fix or not, it's however the safest fix I found. A different fix would be to call UI_popup_block_close before WM_operator_call_ex (in dialog_exec_cb), but not sure how safe this is and want to further investigate if it makes other hacks/fixes redundant.

There's still a crash with --debug-memory that confused the heck out of me (since I always have --debug-memory enabled), but I'll commit fix for that separately.