Debugger: Fix QByteArray/QString overload mixup

And take the opportunity to sprinkle more 'override' over the code.

Change-Id: I8b6b80653ca671e7681b7de2de5ad4288b281ccf
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/debugger/cdb/cdbengine.h

@@ -57,7 +57,7 @@ public:
     typedef std::function<void(const DebuggerResponse &)> CommandHandler;
 
     CdbEngine(const DebuggerRunParameters &sp);
-    ~CdbEngine();
+    ~CdbEngine() override;
 
     // Factory function that returns 0 if the debug engine library cannot be found.