libvirt: ensure defresult is used in virConnectAuthCallbackDefault
libvirt: ensure defresult is used in virConnectAuthCallbackDefault

A previous change to this function's password handling broke the use of
default values for credential types other than VIR_CRED_PASSPHRASE and
VIR_CRED_NOECHOPROMPT.

Reviewed-by: Daniel P. Berrangé <bb938cf255e055ff3507f2627d214e8e62118fcf@redhat.com>
Reviewed-by: Neal Gompa <8135daa3762340227c0c67f1c47ad07a127bd3a3@gmail.com>
Signed-off-by: Matt Coleman <1fa2ef4755a9226cb9a0a4840bd89b158ac71391@datto.com>

olafhering/libvirt,olafhering/libvirt,nertpinx/libvirt,crobinso/libvirt,olafhering/libvirt,nertpinx/libvirt,libvirt/libvirt,jfehlig/libvirt,jardasgit/libvirt,zippy2/libvirt,crobinso/libvirt,crobinso/libvirt,jardasgit/libvirt,jardasgit/libvirt,libvirt/libvirt,jardasgit/libvirt,libvirt/libvirt,olafhering/libvirt,nertpinx/libvirt,jfehlig/libvirt,zippy2/libvirt,nertpinx/libvirt,libvirt/libvirt,crobinso/libvirt,jfehlig/libvirt,jfehlig/libvirt,nertpinx/libvirt,zippy2/libvirt,zippy2/libvirt,jardasgit/libvirt