Fix status message being set to null accidentally
In other words, "account jabber set away Message" resulted in away
status being set, but not "Message".
Fixes trac ticket 1291
This was broken by ac68733ad7a5127395d6367b655a2d9de5d911b5 (3.4.2)
That commit added another call of imc_away_state_find() with the fixed
string "away", so purple protocols can become away by setting away to
any string. But by doing so, it wiped the status message because it's
the same as the name of the away state.
