gtk: Fix return type of RecentChooser.GetUris
gtk: Fix return type of RecentChooser.GetUris

The native function returns a NULL-terminated array of strings, so add
this as a fix-up.

Gankov/gtk-sharp,Gankov/gtk-sharp,akrisiun/gtk-sharp,akrisiun/gtk-sharp,sillsdev/gtk-sharp,antoniusriha/gtk-sharp,akrisiun/gtk-sharp,antoniusriha/gtk-sharp,sillsdev/gtk-sharp,Gankov/gtk-sharp,orion75/gtk-sharp,antoniusriha/gtk-sharp,Gankov/gtk-sharp,orion75/gtk-sharp,Gankov/gtk-sharp,sillsdev/gtk-sharp,openmedicus/gtk-sharp,orion75/gtk-sharp,openmedicus/gtk-sharp,openmedicus/gtk-sharp,openmedicus/gtk-sharp,Gankov/gtk-sharp,orion75/gtk-sharp,orion75/gtk-sharp,openmedicus/gtk-sharp,openmedicus/gtk-sharp,akrisiun/gtk-sharp,openmedicus/gtk-sharp,sillsdev/gtk-sharp,antoniusriha/gtk-sharp,sillsdev/gtk-sharp,akrisiun/gtk-sharp,antoniusriha/gtk-sharp