Don't crash if set_app_info is called before adding metadata
Don't crash if set_app_info is called before adding metadata

set_mime_type, set_is_private, add_group, set_groups, set_icon, etc
all added metadata before using it. If set_app_info was called before
any of those it would crash when trying to access the metadata.

MathieuDuponchelle/glib,endlessm/glib,djdeath/glib,cosimoc/glib,lukasz-skalski/glib,Distrotech/glib,johne53/MB3Glib,ieei/glib,tchakabam/glib,MathieuDuponchelle/glib,tamaskenez/glib,krichter722/glib,krichter722/glib,gale320/glib,cosimoc/glib,mzabaluev/glib,krichter722/glib,mzabaluev/glib,cention-sany/glib,gale320/glib,djdeath/glib,tamaskenez/glib,mzabaluev/glib,gale320/glib,ieei/glib,krichter722/glib,mzabaluev/glib,cention-sany/glib,tchakabam/glib,gale320/glib,lukasz-skalski/glib,Distrotech/glib,johne53/MB3Glib,cention-sany/glib,johne53/MB3Glib,krichter722/glib,tchakabam/glib,endlessm/glib,gale320/glib,djdeath/glib,ieei/glib,johne53/MB3Glib,MathieuDuponchelle/glib,mzabaluev/glib,tamaskenez/glib,djdeath/glib,ieei/glib,Distrotech/glib,tchakabam/glib,tamaskenez/glib,cosimoc/glib,tchakabam/glib,cosimoc/glib,lukasz-skalski/glib,johne53/MB3Glib,MathieuDuponchelle/glib,djdeath/glib,MathieuDuponchelle/glib,endlessm/glib,lukasz-skalski/glib,endlessm/glib,tamaskenez/glib,cention-sany/glib,Distrotech/glib,cosimoc/glib,ieei/glib,johne53/MB3Glib,cention-sany/glib,endlessm/glib,Distrotech/glib,lukasz-skalski/glib