Previously, the warning log was only flushed if creating the db or logging
to stdout.  This meant that under normal circumstances (no db creation,
logging to files) the warning log was never flushed.  This caused a bug
when a warning was printed for each call to the status command where the
warning buffer would grow endlessly, eventually using more and more CPU to
reallocate it.

git-svn-id: https://svn.musicpd.org/mpd/trunk@6660 09075e82-0dd4-0310-85a5-a0d7c8717e4f