We do this as if we happen to not have any manifest whatsoever, but already opened the block file, and the block file already existed and was still valid, it would be emptied out. Only open it if we are actually going to write into it!
- Only process referenced pack files, previously, if an entry in the VPK file was build into a pack of index 128, the code would generate a list of pack files from 0 to 128.
- Added documentation to VPK structure.
