[1.6.7] Heavy weapon psi wield bad lua error

[Horken]

I tried some weird adventurer built, and that went wrong.
When you have a psi-wielded shooter and no mainhand shooter you can activate heavy weapons, but except for shockstaff bad things happen. I got some lua error, and afterwards was no longer capable of shooting at all, no matter what I was wearing.
There probably should be some sanity check for heavy weapons to check that, currently its on_pre_use only checks for heavy ammunition, not for having a shooter equipped.