compiler: fix critical when vala is called without run args
compiler: fix critical when vala is called without run args

https://bugzilla.gnome.org/show_bug.cgi?id=793657

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