The huge UI rework patch removed some obscure logic and special handling of
thread exit messages. It turns out that this was in fact still needed as a
specific exit message of the SyncRunner thread signified the threatmonitor
to quit.
We will want a nicer machinery for this in the future I guess, but fix the
eternal hang on exit by reintroducing a special exit message for the
SyncRunner thread, and return from the infinite monitor loop if SyncRunner
finishes.
Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>
74d580bc68