Block "SMS Default Dialog" on non-phone devices

This change also handles the case where getDefaultSmsApplication returns
null more elegantly, though this is only really possible on a device that
is a tablet (blocked earlier in the method) or a phone device that had no
SMS apps at boot (when we force the setting of an SMS app.)

Bug: 11072894 People app should not launch into default SMS app on tablets
Change-Id: I1e253873e053c21bc1652bd03d7b486aaf9be5e1