Fix Qex6 move

chess/board.go

@@ -1330,6 +1330,11 @@ func getXY(position string) (int, int, error) {
 		y    int
 	)
 	runes := []rune(position)
+
+	if len(runes) != 2 {
+		return -1, -1, fmt.Errorf("square does not exist: %s", position)
+	}
+
 	posX = runes[0]
 	posY = runes[1]
 

chess/game_test.go

@@ -13,4 +13,7 @@ func TestGame001(t *testing.T) {
 
 	// this used to not parse because of the + at the end
 	assertParse(t, b, "d4 d5 Bf4 Nf6 e3 Ne4 Nc3 Nf2 Kxf2 e6 Qg4 Be7 Re1 O-O Kg3 Bh4+")
+
+	// this used to crash because of an out of bounds error (position was parsed as '6')
+	assertMoveError(t, b, "Qex6", "square does not exist")
 }