game_shiplib: enable counter in shiplib_18
game_shiplib: enable counter in shiplib_18

The 68000 assembly function decreases SHIPLIB global
0xc every run of the function, implement this (though
it doesn't seem the counter is used in anything besides
this function)

laanwj/sundog,laanwj/sundog,laanwj/sundog,laanwj/sundog