beautifying the error messages

sql/item.cc

@@ -178,7 +178,7 @@ const char *Item_ident::full_name() const
   char *tmp;
   if (!table_name)
     return field_name ? field_name : name ? name : "tmp_field";
-  if (db_name)
+  if (db_name && db_name[0])
   {
     tmp=(char*) sql_alloc((uint) strlen(db_name)+(uint) strlen(table_name)+
 			  (uint) strlen(field_name)+3);

sql/sql_base.cc

@@ -1707,7 +1707,7 @@ find_field_in_tables(THD *thd, Item_ident *item, TABLE_LIST *tables,
     if (!found_table && report_error)
     {
       char buff[NAME_LEN*2+1];
-      if (db)
+      if (db && db[0])
       {
 	strxnmov(buff,sizeof(buff)-1,db,".",table_name,NullS);
 	table_name=buff;