Fixes a bug that would jam guns entirely (#6470)

# About the pull request

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I couldn't figure out what caused this bug but it was getting kinda bad,
something about alternating akimbo would cause guns to be entirely
disabled, with the current_mag having been ejected, but still marked as
in the gun, but not in the contents, meaning the gun was entirely broke
as you couldnt clear out the mag inside of it cause there was no mag.

this pr just adds a failsafe to prevent this from ever happening

# Explain why it's good for the game

Having your gun becoming entirely unusable and having to just toss it
out cause a bug broke it isnt fun


# Testing Photographs and Procedure

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<summary>Screenshots & Videos</summary>

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# Changelog

:cl:
fix: fixes a bug that fully jammed guns being used in akimbo
/:cl:

code/modules/projectiles/gun.dm

@@ -872,6 +872,8 @@ User can be passed as null, (a gun reloading itself for instance), so we need to
 
 	if(!current_mag || QDELETED(current_mag) || (current_mag.loc != src && !loc_override))
 		cock(user)
+		current_mag = null
+		update_icon()
 		return
 
 	if(drop_override || !user) //If we want to drop it on the ground or there's no user.