mood.c: Don't try twice to activate an invalid mood.

mood.c: Don't try twice to activate an invalid mood.

(Re-)loading a mood by executing the "select" server command fails
if the mood definition is invalid. In this case we first try to
switch back to the old mood, and if this also fails, fall back to
the dummy mood.

If the mood which is currently active has been replaced by an invalid
mood, switching back to the old mood is pointless because this will
try to load the same invalid mood again.

This commit modifies the select callback to load the old mood only
if it is different from the new mood.