PhoneFactory: fall back to default RIL if custom RIL Class fails

If the ro.telephony.ril_class property is set to an invalid class it will cause
Phone to repeatedly FC and make the device unuseable. This allows it to handle the
exceptions gracefully and fall back on the default RIL.

Change-Id: Ic9c309aff173de5267aa7ef633bfff87243f24fd