MainWindow: fix a bug where user/channel actions were enabled even though no user or channel was selected.
MainWindow: fix a bug where user/channel actions were enabled even though no user or channel was selected.

bheart/mumble,unascribed/mumble,SuperNascher/mumble,richard227/mumble,Zopieux/mumble,Natenom/mumble,Keridos/mumble,SuperNascher/mumble,mbax/mumble,SuperNascher/mumble,niko20010/mumble,SuperNascher/mumble,austinliou/mumble,niko20010/mumble,feld/mumble,feld/mumble,austinliou/mumble,richard227/mumble,Zopieux/mumble,Natenom/mumble,ccpgames/mumble,ccpgames/mumble,Natenom/mumble,Lartza/mumble,niko20010/mumble,mbax/mumble,ccpgames/mumble,bheart/mumble,ccpgames/mumble,bheart/mumble,austinliou/mumble,niko20010/mumble,Natenom/mumble,Zopieux/mumble,niko20010/mumble,bheart/mumble,feld/mumble,niko20010/mumble,LuAPi/mumble,mbax/mumble,SuperNascher/mumble,austinliou/mumble,austinliou/mumble,richard227/mumble,mbax/mumble,Githlar/mumble,LuAPi/mumble,unascribed/mumble,mbax/mumble,Keridos/mumble,SuperNascher/mumble,LuAPi/mumble,Natenom/mumble,mbax/mumble,Natenom/mumble,Zopieux/mumble,feld/mumble,Lartza/mumble,niko20010/mumble,Keridos/mumble,feld/mumble,Lartza/mumble,unascribed/mumble,Keridos/mumble,LuAPi/mumble,SuperNascher/mumble,feld/mumble,Lartza/mumble,richard227/mumble,austinliou/mumble,richard227/mumble,bheart/mumble,Lartza/mumble,unascribed/mumble,Lartza/mumble,austinliou/mumble,ccpgames/mumble,Keridos/mumble,ccpgames/mumble,Zopieux/mumble,Githlar/mumble,Keridos/mumble,ccpgames/mumble,Zopieux/mumble,feld/mumble,Zopieux/mumble,feld/mumble,richard227/mumble,LuAPi/mumble,Natenom/mumble,Keridos/mumble,unascribed/mumble,Lartza/mumble,SuperNascher/mumble,Keridos/mumble,ccpgames/mumble,unascribed/mumble,Lartza/mumble,SuperNascher/mumble,mbax/mumble,Githlar/mumble,austinliou/mumble,richard227/mumble,bheart/mumble,niko20010/mumble,unascribed/mumble,Githlar/mumble,bheart/mumble,bheart/mumble,LuAPi/mumble,Zopieux/mumble,LuAPi/mumble,mbax/mumble,LuAPi/mumble,richard227/mumble,unascribed/mumble,Githlar/mumble,Natenom/mumble,Githlar/mumble,LuAPi/mumble,Githlar/mumble,Githlar/mumble