[core] fix memory leak in configparser_merge_data

Release op1 memory on failure; fixes some theoretical memory leaks (a
failure results in early exit anyway).

From: Stefan Bühler <stbuehler@web.de>

git-svn-id: svn://svn.lighttpd.net/lighttpd/branches/lighttpd-1.4.x@3101 152afb58-edef-0310-8abb-c4023f1b3aa9

NEWS

@@ -29,6 +29,7 @@ NEWS
   * [mod_fastcgi,mod_scgi] fix leaking file-descriptor when backend spawning failed (reported by Fortify Open Review Project)
   * [core] improve array API to prevent memory leaks
   * [core] refactor array search; raise array size limit to SSIZE_MAX
+  * [core] fix memory leak in configparser_merge_data
 
 - 1.4.39 - 2016-01-02
   * [core] fix memset_s call (fixes #2698)

src/configparser.y

@@ -71,6 +71,7 @@ data_unset *configparser_merge_data(data_unset *op1, const data_unset *op2) {
       return (data_unset *)ds;
     } else {
       fprintf(stderr, "data type mismatch, cannot merge\n");
+      op1->free(op1);
       return NULL;
     }
   }