WinRT: fixed bug whereby SDL would override an app's default orientation

WinRT apps can set a default, preferred orientation via a .appxmanifest file.
SDL was overriding this on app startup, and making the app use all possible
orientations (landscape and portrait).

Thanks to Eric Wing for the heads up on this!

src/core/winrt/SDL_winrtapp_direct3d.cpp

@@ -126,6 +126,16 @@ static void WINRT_SetDisplayOrientationsPreference(void *userdata, const char *n
 {
     SDL_assert(SDL_strcmp(name, SDL_HINT_ORIENTATIONS) == 0);
 
+    /* HACK: prevent SDL from altering an app's .appxmanifest-set orientation
+     * from being changed on startup, by detecting when SDL_HINT_ORIENTATIONS
+     * is getting registered.
+     *
+     * TODO, WinRT: consider reading in an app's .appxmanifest file, and apply its orientation when 'newValue == NULL'.
+     */
+    if ((oldValue == NULL) && (newValue == NULL)) {
+        return;
+    }
+
     // Start with no orientation flags, then add each in as they're parsed
     // from newValue.
     unsigned int orientationFlags = 0;