apps/ca.c: only output DER with SPKAC input and when -out is chosen

So say the docs

Fixes #8055
Reviewed-by: NMatt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/8368)

(cherry picked from commit 69f6b3ceaba493e70e1296880ea6c93e40714f0f)

apps/ca.c

@@ -722,7 +722,7 @@ end_of_options:
 
     /*****************************************************************/
     if (req || gencrl) {
-        if (spkac_file != NULL) {
+        if (spkac_file != NULL && outfile != NULL) {
             output_der = 1;
             batch = 1;
         }