Another function pair required for serialisation; these ones save

and restore anything vitally important in the game_ui. Most of the
game_ui is expected to be stuff about cursor positions and currently
active mouse drags, so it absolutely _doesn't_ want to be preserved
over a serialisation; but one or two things would be disorienting or
outright wrong to reset, such as the Net origin position and the
Mines death counter.

[originally from svn r6026]

rect.c

@@ -2170,6 +2170,15 @@ static void free_ui(game_ui *ui)
     sfree(ui);
 }
 
+char *encode_ui(game_ui *ui)
+{
+    return NULL;
+}
+
+void decode_ui(game_ui *ui, char *encoding)
+{
+}
+
 static void coord_round(float x, float y, int *xr, int *yr)
 {
     float xs, ys, xv, yv, dx, dy, dist;
@@ -2799,6 +2808,8 @@ const struct game thegame = {
     TRUE, game_text_format,
     new_ui,
     free_ui,
+    encode_ui,
+    decode_ui,
     game_changed_state,
     interpret_move,
     execute_move,