GAsync: Fix GSourceFunc callbacks in virtual methods
GAsync: Fix GSourceFunc callbacks in virtual methods

playya/vala,lovebug356/vala,severinh/vala,tjol/vala-tjol,playya/vala,frida/vala,GNOME/vala,jessevdk/vala,Jc2k/vala,GNOME/vala,xdave/pvala,themiwi/vala,lovebug356/vala,spidermonkdust/vala,tjol/vala-tjol,severinh/vala,spidermonkdust/vala,playya/vala,phako/vala,rvu95/vala,frida/vala,severinh/vala,frida/vala,spidermonkdust/vala,Distrotech/vala,rvu95/vala,themiwi/vala,kamanashisroy/aroop,flobrosch/vala-fixes,phako/vala,Distrotech/vala,kamanashisroy/aroop,Jc2k/vala,jessevdk/vala,GNOME/vala,rvu95/vala,frida/vala,kamanashisroy/aroop,flobrosch/vala-fixes,jessevdk/vala,frida/vala,tjol/vala-tjol,themiwi/vala,flobrosch/vala-fixes,GNOME/vala,Distrotech/vala