Fixed bug with INSERT .. SET db_name.tbl_name.col_name=''

mysql-test/r/insert_set.result

+drop database if exists a;
+create database a;
+use a;
+create table b (c int);
+insert into a.b set a.b.c = '1';
+drop database a;

mysql-test/t/insert_set.test

+#
+# Test of mysqld crash with fully qualified column names
+#
+
+drop database if exists a;
+create database a;
+use a;
+create table b (c int);
+insert into a.b set a.b.c = '1';
+drop database a;

sql/sql_base.cc

@@ -1608,7 +1608,7 @@ find_field_in_tables(THD *thd,Item_field *item,TABLE_LIST *tables)
     for (; tables ; tables=tables->next)
     {
       if (!strcmp(tables->name,table_name) &&
-	  (!db || !strcmp(db,tables->db)))
+	  (!db || !tables->db || !strcmp(db,tables->db)))
       {
 	found_table=1;
 	Field *find=find_field_in_table(thd,tables->table,name,length,