Fixes for updates of KADM5_KVNO but not KEY_DATA and vice-versa.

It turns out that updates of kvno but not key data and vice-versa are
both, allowed and actually done (e.g, in kadmin's ank).  Doing the right
thing in these cases turns out to be a bit tricky, but this commit ought
to do it.

kadmin/del_enctype.c

@@ -106,6 +106,10 @@ del_enctype(void *opt, int argc, char **argv)
     }
 
     free (princ.key_data);
+    if (j == 0) {
+	free(new_key_data);
+	new_key_data = NULL;
+    }
     princ.n_key_data = j;
     princ.key_data   = new_key_data;