Fixed infinite loop in zip_expand_symlink_path().

This patch was from Francois Gouget, who found this bug in MojoSetup's copy
 of the zip archiver code.

src/archiver_zip.c

@@ -669,6 +669,7 @@ static void zip_expand_symlink_path(char *path)
         else
         {
             prevptr = ptr;
+            ptr++;
         } /* else */
     } /* while */
 } /* zip_expand_symlink_path */