mozilla: fix small memory leak

(cherry picked from commit 63ae92da)

projects/mozilla/control/npolibvlc.cpp

@@ -1085,6 +1085,7 @@ void LibvlcPlaylistNPObject::parseOptions(NPObject *obj, int *i_options,
                     }
 
                     options[nOptions++] = stringValue(value);
+                    NPN_ReleaseVariantValue(&value);
                 }
                 *i_options = nOptions;
                 *ppsz_options = options;