Lock orientation while showing destination dialog

Otherwise, we lose the calling Activity's window in the
rotation and cannot get its token needed to set the
wallpaper.

Bug: 139867803
Change-Id: Ic0dd0f95d9615fb3c1e00c2b42c201fe96ecd1a8
diff --git a/src/com/android/wallpaper/picker/PreviewFragment.java b/src/com/android/wallpaper/picker/PreviewFragment.java
index d0d8202..513e7ed 100755
--- a/src/com/android/wallpaper/picker/PreviewFragment.java
+++ b/src/com/android/wallpaper/picker/PreviewFragment.java
@@ -460,7 +460,7 @@
     }
 
     protected void onSetWallpaperClicked(View button) {
-        mWallpaperSetter.requestDestination(getContext(), getFragmentManager(), this,
+        mWallpaperSetter.requestDestination(getActivity(), getFragmentManager(), this,
                 mWallpaper instanceof LiveWallpaperInfo);
     }