Don't use mech default cred when input cred isn't
Don't use mech default cred when input cred isn't

gss_init_sec_context() with input_cred_handle != GSS_C_NO_CREDENTIAL
should NOT proceed if there is no element in the given credential for
the requested mechanism.

madscientist159/heimdal,madscientist159/heimdal,madscientist159/heimdal,madscientist159/heimdal,madscientist159/heimdal,madscientist159/heimdal,madscientist159/heimdal