Check for NumberFormatException while parsing Long string.

In cases where parseLong is passed with a string that is
not long parsable, then NumberFormatException is thrown.
Fix is to catch the NumberFormatException in PhoneAccountRegistrar
while handling the parseLong API.

Change-Id: Ibe4cb23a0c3af769f9934ec8e11834a8c5cd092f
CRs-Fixed: 778493