sources: reorder unsynchronised source status

sources: reorder unsynchronised source status

In the source selection, check for the unsynchronized leap status after
getting sourcestats data. The unsynchronized source status is supposed
to indicate an unsynchronized source that is providing samples, not a
source which doesn't have any samples.

Also, fix the comment describing the status.

Fixes: 4c29f8888c76 ("sources: handle unsynchronized sources in selection")