Hacky fix for the crash of the IO reg view tool.

Reason of the crash: a WM_COMMAND message was being sent for IDC_AUTO_UPDATE_SECS before the WM_INITDIALOG message was sent. I can't figure out why.

desmume/src/windows/IORegView.cpp

@@ -130,6 +130,7 @@ BOOL CALLBACK IoregView_Proc (HWND hwnd, UINT message, WPARAM wParam, LPARAM lPa
 				SendMessage(hwnd, WM_COMMAND, IDC_REFRESH, 0);
 				return 1;
             case WM_COMMAND :
+				if(IORegView == NULL) return 0;
                  switch (LOWORD (wParam))
                  {
                         case IDC_FERMER :