Fix bug #970

Crash on mysql-query_digests=false, mysql-commands_stats=true, and short query

lib/Query_Processor.cpp

@@ -1024,7 +1024,11 @@ void Query_Processor::query_parser_init(SQP_par_t *qp, char *query, int query_le
 #endif /* DEBUG */
 	} else {
 		if (mysql_thread___commands_stats) {
-			qp->query_prefix=strndup(query,32);
+			size_t sl=32;
+			if ((unsigned int)query_length < sl) {
+				sl=query_length;
+			}
+			qp->query_prefix=strndup(query,sl);
 		}
 	}
 };