Fix infinite loop in case an invalid pk3 file has been downloaded from the server. Thanks tjw for reporting (#3074)

code/qcommon/qcommon.h

@@ -605,6 +605,7 @@ qboolean FS_FileExists( const char *file );
 
 qboolean FS_CreatePath (char *OSPath);
 char   *FS_BuildOSPath( const char *base, const char *game, const char *qpath );
+qboolean FS_CompareZipChecksum(const char *zipfile);
 
 int		FS_LoadStack( void );