codegen: Unref GLib.AsyncResult on uncaught errors in coroutines
codegen: Unref GLib.AsyncResult on uncaught errors in coroutines

Ignoring the warning of uncaught error in async methods resulted in
leaking a reference to the scopes GLib.AsyncResult.

https://bugzilla.gnome.org/show_bug.cgi?id=641171

frida/vala,GNOME/vala,frida/vala,GNOME/vala,GNOME/vala,frida/vala,frida/vala,frida/vala,GNOME/vala