WallpaperManager: add NULL pointer check for getCropAndSetWallpaperIntent

Originally the api 'getCropAndSetWallpaperIntent' does not check
whether the parsed parameter is a NULL pointer, as leads to the
whole app crash if it call this api with a null parameter accidentally.
A null pointer check logic is added into its original parameter check
logic, so that this API will throw an IllegalArgumentException if it
is parsed with a null pointer

Change-Id: Ib7de40e571419d09e1a744edc969eb7162766b75
Signed-off-by: houst0nn <houstonn@gmail.com>