Fix dead players sending alliance requests (#1508)

## Description:

Prevent unholly alliances with the undead.

## 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 have read and accepted the CLA aggreement (only required once).

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

IngloriousTom

src/core/game/PlayerImpl.ts

@@ -398,7 +398,7 @@ export class PlayerImpl implements Player {
     if (other === this) {
       return false;
     }
-    if (this.isFriendly(other)) {
+    if (this.isFriendly(other) || !this.isAlive()) {
       return false;
     }
 

tests/AllianceExtensionExecution.test.ts

@@ -32,6 +32,7 @@ describe("AllianceExtensionExecution", () => {
   });
 
   test("Successfully extends existing alliance", () => {
+    jest.spyOn(player1, "canSendAllianceRequest").mockReturnValue(true);
     game.addExecution(new AllianceRequestExecution(player1, player2.id()));
     game.executeNextTick();
     game.executeNextTick();

tests/PlayerImpl.test.ts

@@ -98,4 +98,13 @@ describe("PlayerImpl", () => {
 
     expect(ports.length).toBe(3);
   });
+
+  test("Can't send alliance requests when dead", () => {
+    // conquer other
+    const otherTiles = other.tiles();
+    for (const tile of otherTiles) {
+      player.conquer(tile);
+    }
+    expect(other.canSendAllianceRequest(player)).toBe(false);
+  });
 });