D-Bus: Fix crash on interfaces without methods in GDBus servers
D-Bus: Fix crash on interfaces without methods in GDBus servers

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