ompi/attribute: plug a memory leak in set_value()

OBJ_RELEASE() the previous attribute value if any

Signed-off-by: Gilles Gouaillardet <gilles@rist.or.jp>

ompi/attribute/attribute.c

@@ -1150,6 +1150,7 @@ static int set_value(ompi_attribute_type_t type, void *object,
         if (MPI_SUCCESS != ret) {
             return ret;
         }
+        OBJ_RELEASE(old_attr);
         had_old = true;
     }