Fix nullable struct properties
Fix nullable struct properties

Fixes bug 595587.

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