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/core/execution/ExecutionManager.ts

@@ -1,5 +1,4 @@
 import { Execution, Game } from "../game/Game";
-import { TileRef } from "../game/GameMap";
 import { PseudoRandom } from "../PseudoRandom";
 import { ClientID, GameID, Intent, Turn } from "../Schemas";
 import { simpleHash } from "../Util";
@@ -72,16 +71,12 @@ export class Executor {
           this.mg.ref(intent.x, intent.y),
         );
       case "boat":
-        let src: TileRef | null = null;
-        if (intent.srcX !== null && intent.srcY !== null) {
-          src = this.mg.ref(intent.srcX, intent.srcY);
-        }
         return new TransportShipExecution(
           player,
           intent.targetID,
-          this.mg.ref(intent.dstX, intent.dstY),
+          intent.dst,
           intent.troops,
-          src,
+          intent.src,
         );
       case "allianceRequest":
         return new AllianceRequestExecution(player, intent.recipient);

src/core/execution/MoveWarshipExecution.ts

@@ -9,6 +9,10 @@ export class MoveWarshipExecution implements Execution {
   ) {}
 
   init(mg: Game, ticks: number): void {
+    if (!mg.isValidRef(this.position)) {
+      console.warn(`MoveWarshipExecution: position ${this.position} not valid`);
+      return;
+    }
     const warship = this.owner
       .units(UnitType.Warship)
       .find((u) => u.id() === this.unitId);

src/core/execution/TransportShipExecution.ts

@@ -51,6 +51,16 @@ export class TransportShipExecution implements Execution {
       this.active = false;
       return;
     }
+    if (!mg.isValidRef(this.ref)) {
+      console.warn(`TransportShipExecution: ref ${this.ref} not valid`);
+      this.active = false;
+      return;
+    }
+    if (this.src !== null && !mg.isValidRef(this.src)) {
+      console.warn(`TransportShipExecution: src ${this.src} not valid`);
+      this.active = false;
+      return;
+    }
 
     this.lastMove = ticks;
     this.mg = mg;