Fix horizontal flip for player metasprite

src/player.s

@@ -119,7 +119,7 @@ Player_Update::
     dec [hl]
     ret
 
-; Update sprite OAM entries with current position and direction
+; Update player metasprite with positional data
 update_oam:
     ld hl, PLAYER_DIR
     ld a, [hl-] ; dir (0 = right , $ff = left)
@@ -191,4 +191,22 @@ update_oam:
     inc hl
     ld [hl], c
 
+    ; flip tile indices if necessary
+    ld a, c
+    or c
+    jr z, .done
+
+    ld_OAM_tile hl, SPRITE_OAM_IDX
+    ld [hl], SPRITE_IDX + 1
+
+    ld_OAM_tile hl, SPRITE_OAM_IDX + 1
+    ld [hl], SPRITE_IDX
+
+    ld_OAM_tile hl, SPRITE_OAM_IDX + 2
+    ld [hl], SPRITE_IDX + 3
+
+    ld_OAM_tile hl, SPRITE_OAM_IDX + 3
+    ld [hl], SPRITE_IDX + 2
+
+.done:
     ret