Only reset dim amount when permission was granted

If the permission was never granted, the wallpaper dim amount does not
need to be reset (since it was never changed during testing). This
prevents failures on devices that don't support wallpapers.

Fixes: 224909451
Test: atest android.app.cts.WallpaperManagerTest
Change-Id: Id2e3fdff1e9006ad3e80b52f38915f74462308ec
1 file changed