Add a missing const in unfinished/sokoban.c.

I noticed this when I temporarily enabled compilation of all the
unfinished puzzles while doing the bool trawl.

diff --git a/unfinished/sokoban.c b/unfinished/sokoban.c
index 44332fd15a92a7543c7d237f58aa0f06d26d5a29..7d42a12c5d7d860090c720dbc094cd6483d25ad5 100644 (file)
--- a/unfinished/sokoban.c
+++ b/unfinished/sokoban.c
@@ -957,7 +957,7 @@ struct game_drawstate {
  * subfunction. move_type() returns -1 for an illegal move, 0 for a
  * movement, and 1 for a push.
  */
-int move_type(game_state *state, int dx, int dy)
+int move_type(const game_state *state, int dx, int dy)
 {
     int w = state->p.w, h = state->p.h;
     int px = state->px, py = state->py;