Mech syringe guns don't stop trying to make reagents after the mech is destroyed.

Created by: Faptastic

17:17:28 Runtime detected Cannot read null.total_volume at medical_tools.dm:660 proc name: process (/datum/global_iterator/mech_synth/process) source file: medical_tools.dm,660

If a mech with a syringe gun is set to constantly produce reagents, even after the mech is wrecked the gun will still try to make more, resulting in the above error message every 10 seconds or so.

Steps to reproduce: Make an Odysseus, equip it with syringe gun, set the gun to produce reagents constantly. Proceed to have the mech destroyed and turned into wreckage, experience the above error.

I even deleted the wreckage and it carried on.