apps: make list -help not continue with listing

All the commands return after printing their help.  List doesn't.
This brings them in line.

Reviewed-by: Tim Hudson <tjh@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15211)

apps/list.c

@@ -1560,7 +1560,7 @@ opthelp:
             return 1;
         case OPT_HELP:
             opt_help(list_options);
-            break;
+            return 0;
         case OPT_ONE:
             one = 1;
             break;