Nickname tab completion is broken

• gajim nightly

Actual behavior / observations

Pressing Tab without having typed anything into message input field:

• nicks produced are not in alphabetical order
• nicks are produced in consistent order (same each time when retrying)
• many nicks are not present (seems to cycle through a cache of all nicks ever seen in channel) and were not present in current gajim run

Pressing Tab after typing some characters:

• does honor typed characters in all completions
• does not necessarily complete to most recently matching nick
• many nicks produced are not present and were not present in current gajim run