SupportLeanbackDemos: Fixed password crash when no payment is selected

The second Guided Step fragment crashed when a password was entered but
no credit card info was selected, because it was trying to extract "Visa"
or "Master" substrings from an empty string. Put a check for string
sizes before this extraction is performed.

Change-Id: I9b93a302f5f855b1853885ff4e5fc9a04c200766
2 files changed