Dominosa: require the two halves of a domino to be adjacent

Also that a line indicating no domino be between adjacent squares.
Without this, execute_move would allow you to place dominos and edges
between any pair ot squares, and then generate assertion failures
("execute_move: Assertion `d2 - w >= 0' failed." and "execute_move:
Assertion `d1 - w >= 0' failed.") when a domino was placed over an
invalid edge.  This example save file demonstrates the problem:

SAVEFILE:41:Simon Tatham's Portable Puzzle Collection
GAME    :8:Dominosa
PARAMS  :1:6
CPARAMS :1:6
DESC    :56:55521461210004364611033535444421636022603153156422620503
NSTATES :1:3
STATEPOS:1:3
MOVE    :4:E0,2
MOVE    :4:D0,2

1 files changed, 4 insertions, 2 deletions

diff --git a/dominosa.c b/dominosa.c
index e60cb46..61b345e 100644
--- a/dominosa.c
+++ b/dominosa.c
@@ -2896,7 +2896,8 @@ static game_state *execute_move(const game_state *state, const char *move)
             move++;
         } else if (move[0] == 'D' &&
                    sscanf(move+1, "%d,%d%n", &d1, &d2, &p) == 2 &&
-                   d1 >= 0 && d1 < wh && d2 >= 0 && d2 < wh && d1 < d2) {
+                   d1 >= 0 && d1 < wh && d2 >= 0 && d2 < wh && d1 < d2 &&
+                   (d2 - d1 == 1 || d2 - d1 == w)) {
 
             /*
              * Toggle domino presence between d1 and d2.
@@ -2964,7 +2965,8 @@ static game_state *execute_move(const game_state *state, const char *move)
         } else if (move[0] == 'E' &&
                    sscanf(move+1, "%d,%d%n", &d1, &d2, &p) == 2 &&
                    d1 >= 0 && d1 < wh && d2 >= 0 && d2 < wh && d1 < d2 &&
-                   ret->grid[d1] == d1 && ret->grid[d2] == d2) {
+                   ret->grid[d1] == d1 && ret->grid[d2] == d2 &&
+                   (d2 - d1 == 1 || d2 - d1 == w)) {
 
             /*
              * Toggle edge presence between d1 and d2.