Do not retrieve err msg when connection is established successfully (#20486)

* Do not retrieve err msg when connection is established successfully to avoid exception.

* Restore check script for lua installation.

examples/lua/build.sh

@@ -4,5 +4,5 @@ if [ "$lua_header_installed" = "0" ]; then
   sudo apt install -y liblua5.3-dev
 fi
 
-gcc -std=c99 lua_connector.c -fPIC -shared -o luaconnector.so -Wall -ltaos -I/usr/include/lua5.3 -I../../include/client
+gcc -g -std=c99 lua_connector.c -fPIC -shared -o luaconnector.so -Wall -ltaos -I/usr/include/lua5.3 -I../../include/client
 

examples/lua/lua51/lua_connector51.c

@@ -67,7 +67,7 @@ static int l_connect(lua_State *L){
 
   taos = taos_connect(host, user,password,database, port);
   if (taos == NULL) {
-    printf("failed to connect server, reason:%s\n", taos_errstr(taos));
+    //printf("failed to connect server, reason:%s\n", taos_errstr(taos));
     
     lua_pushinteger(L, -1);
     lua_setfield(L, table_index, "code");
@@ -79,7 +79,7 @@ static int l_connect(lua_State *L){
     // printf("success to connect server\n");
     lua_pushinteger(L, 0);
     lua_setfield(L, table_index, "code");
-    lua_pushstring(L, taos_errstr(taos));
+    lua_pushstring(L, "success");
     lua_setfield(L, table_index, "error");    
     lua_pushlightuserdata(L,taos);
     lua_setfield(L, table_index, "conn");

examples/lua/lua_connector.c

@@ -67,8 +67,7 @@ static int l_connect(lua_State *L){
 
   taos = taos_connect(host, user,password,database, port);
   if (taos == NULL) {
-    printf("failed to connect server, reason:%s\n", taos_errstr(taos));
-    
+//  printf("failed to connect server, reason:%s\n", taos_errstr(NULL));
     lua_pushinteger(L, -1);
     lua_setfield(L, table_index, "code");
     lua_pushstring(L, taos_errstr(taos));
@@ -79,7 +78,7 @@ static int l_connect(lua_State *L){
     // printf("success to connect server\n");
     lua_pushinteger(L, 0);
     lua_setfield(L, table_index, "code");
-    lua_pushstring(L, taos_errstr(taos));
+    lua_pushstring(L, "success");
     lua_setfield(L, table_index, "error");    
     lua_pushlightuserdata(L,taos);
     lua_setfield(L, table_index, "conn");