user-accounts: Fix password dialog crashes
Currently, the password_entry_timeout() callback can be called even after the dialog disposal, which leads to segfaults. This is because the corresponding source ids can be cleared in some cases without removing the sources. Let's prevent direct calls of password_entry_timeout() without destroying the source ids in order to fix this issue.
Fixes: #760 (closed)
(cherry picked from commit 29367abb)