after review fixes

sql/sql_select.cc

@@ -3267,11 +3267,11 @@ static bool create_ref_for_key(JOIN *join, JOIN_TAB *j, KEYUSE *org_keyuse,
 				  &keyinfo->key_part[i],
 				  (char*) key_buff,maybe_null);
       /*
-	Remmeber if we are going to use REF_OR_NULL
+	Remeber if we are going to use REF_OR_NULL
 	But only if field _really_ can be null i.e. we force JT_REF
 	instead of JT_REF_OR_NULL in case if field can't be null
       */
-      if (keyuse->optimize & KEY_OPTIMIZE_REF_OR_NULL && maybe_null)
+      if ((keyuse->optimize & KEY_OPTIMIZE_REF_OR_NULL) && maybe_null)
 	null_ref_key= key_buff;
       key_buff+=keyinfo->key_part[i].store_length;
     }