Fix BSP import error when q3map2_type is missing from gamepack xml
Using File -> Import... to import a BSP using a gamepack that does not specify q3map2_type (such as the Quake 3 gamepack) resulted in a fatal error:
runtime error: game attribute "q3map2_type" not found in "q3.game"
The code already has a fallback to use type "quake3" if q3map2_type is missing so don't require gamepacks to specify it.