Merge pull request #2531 from taosdata/hotfix/fix_rpc_issue

fixbug use_after_free

src/rpc/src/rpcMain.c

@@ -1529,10 +1529,10 @@ static void rpcAddRef(SRpcInfo *pRpc)
 static void rpcDecRef(SRpcInfo *pRpc)
 { 
   if (atomic_sub_fetch_32(&pRpc->refCount, 1) == 0) {
+    rpcCloseConnCache(pRpc->pCache);
     taosHashCleanup(pRpc->hash);
     taosTmrCleanUp(pRpc->tmrCtrl);
     taosIdPoolCleanUp(pRpc->idPool);
-    rpcCloseConnCache(pRpc->pCache);
 
     tfree(pRpc->connList);
     pthread_mutex_destroy(&pRpc->mutex);