one more unisialized variable fix

src/ua_connection.c

@@ -20,6 +20,7 @@ void UA_Connection_init(UA_Connection *connection) {
     connection->close = UA_NULL;
     connection->recv = UA_NULL;
     connection->getBuffer = UA_NULL;
+    connection->releaseBuffer = UA_NULL;
 }
 
 void UA_Connection_deleteMembers(UA_Connection *connection) {