libvaladoc: Properly support the output of async constructors
libvaladoc: Properly support the output of async constructors

Fixes https://gitlab.gnome.org/GNOME/vala/issues/753

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