applets/kicker: use correct fallback in AppEntry ctor
Reason for the change
Constructing an AppEntry (for non-preferred:// schemes), we first try serviceByStorageId on the path part of the url, and if that does not find anything, we try again with the value of m_id... except that m_id only stores the supplied id in case of preferred:// urls, and is left default-initialized otherwise, so this always looks up the service for empty string, which is not particularly useful.
Instead, look it up by the id that was passed to the ctor. This makes malformed .desktop file names containing the character ":" somewhat work again. (This is disallowed by the spec, but some software may produce them including, unfortunately, kmenuedit.) They're still broken in all sorts of weird ways, but at least they will show up when favorited like in 6.6, rather than just fail.
Test plan
Create a .desktop file with a malformed name like "Test: 1.desktop" using kmenuedit (by typing "Test: 1") in the dialog when adding a new entry).
Try to add this to your favorites.
In 6.6, this works, but is broken: you can't unfavorite it anymore
On current master, this doesn't work at all - the favorite doesn't show up.
Obviously both are not good (and 520894 should be fixed), but if people have added such a favorite in the past, we shouldn't just break it.
Screenshots or screen recordings
N/A