Don't access fingerprint service when unavailable

For devices which don't have a fingerprint service, an attempt to
get the fingerprint system service creates an Error.  We want to
avoid this, so we add a check prior to the access.

Bug: 174800840
Test: Bugreport on a non-fingerprint device no longer has a "No service published for: fingerprint" Error

Change-Id: I2e96e8cb8cc45ab86d0b2bfa9d651c85b58cd0da