Bug fixes for alternative zip layout and define to toggle it on

Fixes a couple of bugs with the zip system and adds a define to use the alternative zip support where you can define your directories and files inside the zip just like you would on disk instead of the default zip support that treats the zip as an extra directory.  Just uncomment #define TORQUE_ZIP_DISK_LAYOUT at the top of platform/platformVolume.cpp or add the define to torqueConfig.h