Fix NPE in LauncherPreviewRenderer.

The LauncherBinder is null in LauncherPreviewRenderer, which was
causing an NPE in LoaderTask.

Bug: 279347305
Test: Used logs to verify that the LauncherPreviewRenderer was actually
loading using the LoaderTask. Most of the time, it does not, so that is
why I didn't catch this before pushing it.

Change-Id: Ic5b45abfdeb73a4bbe1f521ae4d627b6cfcfec54