Fix some memory leaks

Free some objects that were allocated with new but not deleted, and in
one case, do not set a pointer to nullptr before deleting, as this
results in a memory leak due to memory allocated not being freed.

src/frontend/qt_sdl/CameraManager.cpp

@@ -146,6 +146,7 @@ CameraManager::~CameraManager()
     // save settings here?
 
     delete[] frameBuffer;
+    delete[] tempFrameBuffer;
 }
 
 void CameraManager::init()