autorun-manager: Fix 'destroy' handler of resident source

autorun-manager: Fix 'destroy' handler of resident source

If the resident source is destroyed, it should be recreated
immediately, so that it is available when another volume is
mounted. However, we only connect to the 'destroy' signal
on the original source, not on newly created ones. As a result,
the resident source only works twice, after that it shows up
without icon and an empty notification.

Fix by always connecting to the source's 'destroy' signal.