- Fix crash when sorting a TBL table with thread=yes.

This was because Tablist can be NULL when no lacal tables are in the list.
  modified:   storage/connect/tabtbl.cpp
  modified:   storage/connect/mysql-test/connect/r/tbl.result
  modified:   storage/connect/mysql-test/connect/t/tbl.test

storage/connect/mysql-test/connect/r/tbl.result

@@ -153,7 +153,7 @@ SELECT * FROM t2;
 v
 22
 CREATE TABLE total (v BIGINT(20) UNSIGNED NOT NULL) ENGINE=CONNECT TABLE_TYPE=TBL TABLE_LIST='t1,t2' OPTION_LIST='thread=yes,port=PORT';;
-SELECT * FROM total;
+SELECT * FROM total order by v desc;
 v
 22
 11

storage/connect/mysql-test/connect/t/tbl.test

@@ -63,7 +63,7 @@ SELECT * FROM t2;
 
 --replace_result $PORT PORT
 --eval CREATE TABLE total (v BIGINT(20) UNSIGNED NOT NULL) ENGINE=CONNECT TABLE_TYPE=TBL TABLE_LIST='t1,t2' OPTION_LIST='thread=yes,port=$PORT';
-SELECT * FROM total;
+SELECT * FROM total order by v desc;
 
 DROP TABLE total;
 DROP TABLE t1;

storage/connect/tabtbl.cpp

@@ -607,7 +607,7 @@ void TDBTBM::ResetDB(void)
   for (PTABLE tabp = Tablist; tabp; tabp = tabp->GetNext())
     ((PTDBASE)tabp->GetTo_Tdb())->ResetDB();
 
-  Tdbp = (PTDBASE)Tablist->GetTo_Tdb();
+  Tdbp = (Tablist) ? (PTDBASE)Tablist->GetTo_Tdb() : NULL;
   Crp = 0;
   } // end of ResetDB
 
@@ -679,7 +679,7 @@ bool TDBTBM::OpenDB(PGLOBAL g)
     /*  Table already open, replace it at its beginning.               */
     /*******************************************************************/
     ResetDB();
-    return Tdbp->OpenDB(g);  // Re-open fist table
+    return (Tdbp) ? Tdbp->OpenDB(g) : false;  // Re-open fist table
     } // endif use
 
 #if 0