Build fix for compiling against minizip.

code/Common/ZipArchiveIOSystem.cpp

@@ -196,7 +196,9 @@ zlib_filefunc_def IOSystem2Unzip::get(IOSystem *pIOHandler) {
     zlib_filefunc_def mapping;
 
     mapping.zopen_file = (open_file_func)open;
+#ifdef _UNZ_H
     mapping.zopendisk_file = (opendisk_file_func)opendisk;
+#endif
     mapping.zread_file = (read_file_func)read;
     mapping.zwrite_file = (write_file_func)write;
     mapping.ztell_file = (tell_file_func)tell;