Fixed leak upon duped serverlist updates

src/core/ext/lb_policy/grpclb/grpclb.c

@@ -1238,12 +1238,15 @@ static void lb_on_response_received(grpc_exec_ctx *exec_ctx, void *arg,
             gpr_log(GPR_INFO,
                     "Incoming server list identical to current, ignoring.");
           }
+          grpc_grpclb_destroy_serverlist(serverlist);
         } else { /* new serverlist */
           if (glb_policy->serverlist != NULL) {
             /* dispose of the old serverlist */
             grpc_grpclb_destroy_serverlist(glb_policy->serverlist);
           }
-          /* and update the copy in the glb_lb_policy instance */
+          /* and update the copy in the glb_lb_policy instance. This serverlist
+           * instance will be destroyed either upon the next update or in
+           * glb_destroy() */
           glb_policy->serverlist = serverlist;
 
           rr_handover_locked(exec_ctx, glb_policy);