Debugger: Guard DebuggerPlugin::m_currentEngine with QPointer

Change-Id: Id0bcca4ca2dba21409e37197269b8166070cf572
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/debugger/debuggerplugin.cpp

@@ -1007,7 +1007,7 @@ public:
 
     SnapshotHandler *m_snapshotHandler = 0;
     bool m_shuttingDown = false;
-    DebuggerEngine *m_currentEngine = 0;
+    QPointer<DebuggerEngine> m_currentEngine;
     DebuggerSettings *m_debuggerSettings = 0;
     QStringList m_arguments;
     DebuggerToolTipManager m_toolTipManager;