Make encode_ui() and decode_ui() optional in back-ends

The majority of back-ends define encode_ui() to return NULL and
decode_ui() to do nothing.  This commit allows them to instead specify
the relevant function pointers as NULL, in which case the mid-end won't
try to call them.

I'm planning to add a parameter to decode_ui(), and if I'm going to have
to touch every back-end's version of decode_ui(), I may as well ensure
that most of them never need to be touched again.  And obviously
encode_ui() should go the same way for symmetry.

1 files changed, 2 insertions, 2 deletions

diff --git a/midend.c b/midend.c
index e66d15a..2e49e8d 100644
--- a/midend.c
+++ b/midend.c
@@ -2204,7 +2204,7 @@ void midend_serialise(midend *me,
     /*
      * Any required serialisation of the game_ui.
      */
-    if (me->ui) {
+    if (me->ui && me->ourgame->encode_ui) {
         char *s = me->ourgame->encode_ui(me->ui);
         if (s) {
             wr("UI", s);
@@ -2541,7 +2541,7 @@ static const char *midend_deserialise_internal(
     }
 
     data.ui = me->ourgame->new_ui(data.states[0].state);
-    if (data.uistr)
+    if (data.uistr && me->ourgame->decode_ui)
         me->ourgame->decode_ui(data.ui, data.uistr);
 
     /*