bug #1945. item(expression)->name=0, crash in find_item_in_list

mysql-test/r/order_by.result

@@ -542,3 +542,7 @@ a	b
 1	2
 5	NULL
 DROP TABLE t1;
+CREATE TABLE t1 (a INT, b INT);
+SET @id=0;
+UPDATE t1 SET a=0 ORDER BY (a=@id), b;
+DROP TABLE t1;

mysql-test/t/order_by.test

@@ -345,3 +345,11 @@ SELECT * FROM t1 ORDER BY (a + b);
 SELECT * FROM t1 ORDER BY (a + b) DESC;
 DROP TABLE t1;
 
+#
+# Bug #1945 - Crashing bug with bad User Variables in UPDATE ... ORDER BY ...
+#
+CREATE TABLE t1 (a INT, b INT);
+SET @id=0;
+UPDATE t1 SET a=0 ORDER BY (a=@id), b;
+DROP TABLE t1;
+

sql/sql_base.cc

@@ -1837,7 +1837,7 @@ find_item_in_list(Item *find,List<Item> &items)
       }
     }
     else if (!table_name && (item->eq(find,0) ||
-			     find->name &&
+			     find->name && item->name &&
 			     !my_strcasecmp(item->name,find->name)))
     {
       found=li.ref();