dirmngr: Emit SOURCE status also on NO_DATA.

* dirmngr/ks-engine-hkp.c (ks_hkp_search): Send SOURCE status also on
NO DATA error.
(ks_hkp_get): Ditto.
* g10/call-dirmngr.c (gpg_dirmngr_ks_search): Print "data source" info
also on error.
(gpg_dirmngr_ks_get): Ditto.

If a keyserver does not return any data it can be useful to know which
keyserver out of the pool answered.

(cherry picked from commit bee65edfbc8cc2c369e5941cc9d1a01a0519b388)

• Signed-off-by: Werner Koch <wk@gnupg.org>