[controller dialog] Fix Coverty CID 152106 introduced in 921862e

Defect was:

*** CID 152106:  Uninitialized members  (UNINIT_CTOR)
GUIConfigurationWizard.cpp: 41 in GAME::CGUIConfigurationWizard::CGUIConfigurationWizard()()
35     #define SKIPPING_DETECTION_MS  200
36
37     CGUIConfigurationWizard::CGUIConfigurationWizard() :
38       CThread("GUIConfigurationWizard")
39     {
40       InitializeState();
>>>     CID 152106:  Uninitialized members  (UNINIT_CTOR)
>>>     Non-static class member "m_callback" is not initialized in this constructor nor in any functions that it calls.
41     }
42
43     void CGUIConfigurationWizard::InitializeState(void)
44     {
45       m_currentButton = nullptr;
46       m_currentDirection = JOYSTICK::ANALOG_STICK_DIRECTION::UNKNOWN;

xbmc/games/controllers/windows/GUIConfigurationWizard.cpp

@@ -36,6 +36,7 @@ using namespace GAME;
 
 CGUIConfigurationWizard::CGUIConfigurationWizard() :
   CThread("GUIConfigurationWizard"),
+  m_callback(nullptr),
   m_bInMotion(false)
 {
   InitializeState();