BUG#12532: Added more memory in malloc for slave query cache

sql/log_event.cc:
  Added memory to malloc
sql/sql_cache.cc:
  Added comment

sql/log_event.cc

@@ -1330,7 +1330,13 @@ Query_log_event::Query_log_event(const char* buf, uint event_len,
   
   if (!(start= data_buf = (char*) my_malloc(catalog_len + 1 +
                                             time_zone_len + 1 +
-                                            data_len + 1, MYF(MY_WME))))
+                                            data_len + 1 +
+#ifndef MYSQL_CLIENT
+#ifdef HAVE_QUERY_CACHE
+					    QUERY_CACHE_FLAGS_SIZE +
+#endif
+#endif
+					    db_len + 1, MYF(MY_WME))))
     DBUG_VOID_RETURN;
   if (catalog_len)                                  // If catalog is given
   {

sql/sql_cache.cc

@@ -923,6 +923,10 @@ sql mode: 0x%lx, sort len: %lu, conncat len: %lu",
 	0	The query was cached and user was sent the result.
 	-1	The query was cached but we didn't have rights to use it.
 		No error is sent to the client yet.
+
+  NOTE
+  This method requires that sql points to allocated memory of size:
+  tot_length= query_length + thd->db_length + 1 + QUERY_CACHE_FLAGS_SIZE;
 */
 
 int