Fix an undefined return value in ksba_cert_get_digest_algo.

* src/cert.c (ksba_cert_get_digest_algo): Set ALGO in the error case.
* tests/cert-basic.c (one_file): Take care of printf which does not
handle NULL for %s
--

GnuPG-bug-id: 2343
Reported-by: Pascal Cuoq

src/cert.c

@@ -464,7 +464,10 @@ ksba_cert_get_digest_algo (ksba_cert_t cert)
 
   n = _ksba_asn_find_node (cert->root, "Certificate.signatureAlgorithm");
   if (!n || n->off == -1)
-    err = gpg_error (GPG_ERR_UNKNOWN_ALGORITHM);
+    {
+      algo = NULL;
+      err = gpg_error (GPG_ERR_UNKNOWN_ALGORITHM);
+    }
   else
     err = _ksba_parse_algorithm_identifier (cert->image + n->off,
                                             n->nhdr + n->len, &nread, &algo);

tests/cert-basic.c

@@ -448,7 +448,8 @@ one_file (const char *fname)
 
   oid = ksba_cert_get_digest_algo (cert);
   s = get_oid_desc (oid);
-  printf ("  hash algo.: %s%s%s%s\n", oid, s?" (":"",s?s:"",s?")":"");
+  printf ("  hash algo.: %s%s%s%s\n",
+          oid?oid:"(null)", s?" (":"",s?s:"",s?")":"");
 
   /* Under Windows the _ksba_keyinfo_from_sexp are not exported.  */
 #ifndef __WIN32