Fix possible NPE on showDialpadChooser()

NPE happens when DialtactsActivity#onNewIntent() is called before
DialpadFragment#onCreateView() is called (which may happen if it is not
attached yet), and DialpadFragment#configureScreenFromIntent()
is called before View objects point to something meaningful.

onCreateView() calls configureScreenFromIntent(), so just ignore the too
early request.

Bug: 5157905
Change-Id: I90eb6ac788fbef4d37527ac224561fba67c058fd