Fix FC caused by NullPointerException

Under certain circumstances, setupKeypad() was called from
updateDialer() *before* the keypad's Views were initialized,
causing the app to force-close.
This patch moves the null check from onCreate() to setupKeypad()
itself, so as to prevent a NullPointerException when called
from updateDialer().

Change-Id: Ide8998ccccb66415ea2d2f819cd542f48466fe09