Don't start game entity loops at index 1

Skip all players or none.
Fix in g_svcmds.c copied from @exidl.
Add trap_FS_Tell to game and cgame VMs
Fix VM FOpenFile( FS_READ ) files seeking twice in FS_Seek
Remove unused variable baseOffset from fsh[]
Support FS_SEEK_END and negative offset for zipped files in FS_Seek

Use FS_SEEK_END in sound code instead of working around it.
If FS_SEEK_SET and going to current position, just return.
Try to protect FS VM syscalls from bad input