Fix flammethrower reloading

fixes #5355

Does it even make sense to add a "normal" spare magazine used by "normal" guns to to hold "normal" ammunition to a flamethrower? Nonetheless, this PR fixes that.

It works only with the reload command, not through `game::handle_liquid`.

It also fixes a bug, that has been reported http://smf.cataclysmdda.com/index.php?topic=3002 :
when reloading a flamethrower uses up all the contents of a container, that container gets deleted (tested with plastic bottle).


Another thing: removing the spare mag while it's loaded will put the gasoline into inventory *without* a container! - fixed

And btw. you can reload a chainsaw/flashlight even when it is already fully loaded. It does not increase the charges, but takes time and shows a message.