Cleaning up mpd_addConstraintSearch.  Now correctly fails on error.
Cleaning up mpd_addConstraintSearch.  Now correctly fails on error.

git-svn-id: 5dea4be1dbd453f88943894215a4d7951dc0947d@4945 09075e82-0dd4-0310-85a5-a0d7c8717e4f
OpenInkpot-archive/iplinux-libmpdclient,cmende/libmpdclient,sl0th/libmpdclient,cmende/libmpdclient,yusiwen/libmpdclient,jagleeso/libmpdclient,jagleeso/libmpdclient,sl0th/libmpdclient,psych0tik/libmpdclient2,OpenInkpot-archive/iplinux-libmpdclient,yusiwen/libmpdclient,psych0tik/libmpdclient2,jagleeso/libmpdclient,jwise/libmpdclient,yusiwen/libmpdclient,jwise/libmpdclient,jwise/libmpdclient,cmende/libmpdclient,sl0th/libmpdclient