Bugfix: don't allow other players to move warships (#879)

## Description:
The MoveWarshipExecution now verifies that the player who requested to
move owns the warship. This prevents players from moving other players'
warships.

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [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

tests/Warship.test.ts

@@ -175,7 +175,7 @@ describe("Warship", () => {
     game.addExecution(new WarshipExecution(warship));
 
     game.addExecution(
-      new MoveWarshipExecution(warship.id(), game.ref(coastX + 5, 15)),
+      new MoveWarshipExecution(player1, warship.id(), game.ref(coastX + 5, 15)),
     );
 
     executeTicks(game, 10);
@@ -211,4 +211,52 @@ describe("Warship", () => {
     // Trade ship should not be captured
     expect(tradeShip.owner().id()).toBe(player2.id());
   });
+
+  test("MoveWarshipExecution fails if player is not the owner", async () => {
+    const originalPatrolTile = game.ref(coastX + 1, 10);
+    const warship = player1.buildUnit(
+      UnitType.Warship,
+      game.ref(coastX + 1, 5),
+      {
+        patrolTile: originalPatrolTile,
+      },
+    );
+    new MoveWarshipExecution(
+      player2,
+      warship.id(),
+      game.ref(coastX + 5, 15),
+    ).init(game, 0);
+    expect(warship.patrolTile()).toBe(originalPatrolTile);
+  });
+
+  test("MoveWarshipExecution fails if warship is not active", async () => {
+    const originalPatrolTile = game.ref(coastX + 1, 10);
+    const warship = player1.buildUnit(
+      UnitType.Warship,
+      game.ref(coastX + 1, 5),
+      {
+        patrolTile: originalPatrolTile,
+      },
+    );
+    warship.delete();
+    new MoveWarshipExecution(
+      player1,
+      warship.id(),
+      game.ref(coastX + 5, 15),
+    ).init(game, 0);
+    expect(warship.patrolTile()).toBe(originalPatrolTile);
+  });
+
+  test("MoveWarshipExecution fails gracefully if warship not found", async () => {
+    const exec = new MoveWarshipExecution(
+      player1,
+      123,
+      game.ref(coastX + 5, 15),
+    );
+
+    // Verify that no error is thrown.
+    exec.init(game, 0);
+
+    expect(exec.isActive()).toBe(false);
+  });
 });