Telephony: Fix NPE while opening allowed number.

Trying to edit existing allowed number caused NPE:

mNameField and mNumberField setText caused TextWatcher afterTextChanged
event while mButton is still null. So set mButton before setTexts.

Change-Id: If444e2d69c77bc10094a1dfd3fc6b700509c6128
Merge remote-tracking branch 'cm/cm-11.0' into kitkat