Fixes

There are two problems:
1. On Debian i had seen wrong sprites in battlescape (in Mutton Commander, Sectopod HWP mods) while generic sprites was shown correctly. Later it was obviously: readdir(3) makes no warranty to return sorted order of files, thu the list of files threated as a sorted one (in Windows, probably it returns sornetd, dut not in Linux).

2. I've enabled Gun Melee mod and noticed, that hit consumes ammo, and when there are no more ammo, the game crashed into segfault. The target code looked very strange. I know no melee weapon, which consumes the ammo. Maybe this code added for some mod? Anyway, after patching it works for me. :-)
instead of removing this code block, add a sanity check for _ammo