fix debug assert statement

src/board.rs

@@ -32,7 +32,11 @@ impl<T> PosMap<T> {
     pub fn get(&self, row: usize, col: usize) -> &T {
         let index = row * BOARD_SIZE + col;
 
-        debug_assert!(index > BOARD_AREA + 1, "index out of range");
+        debug_assert!(
+            BOARD_AREA + 1 >= index,
+            "index out of range, was: {}",
+            index
+        );
 
         unsafe { self.0.get_unchecked(index) }
     }