pki: Fix memory leak of blob on error

CID #1419377

Signed-off-by: Andreas Schneider <asn@cryptomilk.org>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>

src/pki.c

@@ -2293,6 +2293,7 @@ int ssh_pki_import_signature_blob(const ssh_string sig_blob,
         rc = ssh_buffer_unpack(buf, "bd", &flags, &counter);
         if (rc < 0) {
             SSH_BUFFER_FREE(buf);
+            SSH_STRING_FREE(blob);
             return SSH_ERROR;
         }
     }