fix bad tile crash (#1237)

## Description:

Sending invalid coords can cause game to crash. Make sure to validate
tile ref.

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [x] I understand that submitting code with bugs that could have been
caught through manual testing blocks releases and new features for all
contributors

## Please put your Discord username so you can be contacted if a bug or
regression is found:
evan

src/client/graphics/layers/PlayerActionHandler.ts

@@ -48,13 +48,13 @@ export class PlayerActionHandler {
   handleBoatAttack(
     player: PlayerView,
     targetId: PlayerID | null,
-    targetCell: Cell,
-    spawnTile: Cell | null,
+    targetTile: TileRef,
+    spawnTile: TileRef | null,
   ) {
     this.eventBus.emit(
       new SendBoatAttackIntentEvent(
         targetId,
-        targetCell,
+        targetTile,
         this.uiState.attackRatio * player.troops(),
         spawnTile,
       ),