PGPUID.is_primary should be False if no selfsig can be found
PGPUID.is_primary should be False if no selfsig can be found

In some circumstances, no selfsig will be available.  This change
ensures that is_primary doesn't raise an exception in those
circumstances.

Signed-off-by: Daniel Kahn Gillmor <b1356865a0eefd1fb76a8b663fad027be4bc9b61@fifthhorseman.net>

SecurityInnovation/PGPy,SecurityInnovation/PGPy,SecurityInnovation/PGPy