debugger: empty list of fetched variables at the end of the full cycle

The original logic was faulty but worked better in the presence of the
original "extra layoutChanged()" hack which is replaced now.

src/plugins/debugger/gdb/pythongdbengine.cpp

@@ -51,7 +51,7 @@ void GdbEngine::updateLocalsPython(const QByteArray &varList)
     PRECONDITION;
     m_processedNames.clear();
 
-    manager()->watchHandler()->beginCycle(true);
+    manager()->watchHandler()->beginCycle();
     //m_toolTipExpression.clear();
     WatchHandler *handler = m_manager->watchHandler();