IosToolTaskAdapter: Don't leak the IosToolHandler on destruction

The TaskAdapter may be destructed at any point in time,
even when the task is still running (i.e. when the task tree
was canceled). Make sure the internal IosToolHandler gets
deleted in this case.

Amends 150441bf88

Change-Id: I1ae4d324390c38d4faf9ec32f83c66295ed18532
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/ios/iostoolhandler.h

@@ -82,7 +82,7 @@ public:
 
 private:
     friend class IosToolTaskAdapter;
-    IosToolHandler *m_iosToolHandler = nullptr;
+    std::unique_ptr<IosToolHandler> m_iosToolHandler;
     StartHandler m_startHandler;
     Internal::IosDeviceType m_deviceType = Internal::IosDeviceType::IosDevice;
 };