MobjDamage hook doesn't expose damageType if no objectType is given

Simply put, I was coding in some stuff which requires the damageType stuff, but which could apply to multiple enemies, bosses or even players... And after some testing, I noticed the damageType was always being sent as a nil value. So I checked the source code, and... I noticed that the damageType isn't exposed if it's a general hook.

This issue was addressed a week ago by Monster Iestyn.
Here's the relevant commit.