Validate spawn tile (#1512)

## Description:

Enforce valid tile during spawn, to prevent the game from crashing for
all players.

## 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
- [ ] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [ ] I have read and accepted the CLA aggreement (only required once).

src/client/graphics/layers/BuildMenu.ts

@@ -15,7 +15,6 @@ import { translateText } from "../../../client/Utils";
 import { EventBus } from "../../../core/EventBus";
 import {
   BuildableUnit,
-  Cell,
   Gold,
   PlayerActions,
   UnitType,
@@ -396,12 +395,7 @@ export class BuildMenu extends LitElement implements Layer {
         ),
       );
     } else if (buildableUnit.canBuild) {
-      this.eventBus.emit(
-        new BuildUnitIntentEvent(
-          buildableUnit.type,
-          new Cell(this.game.x(tile), this.game.y(tile)),
-        ),
-      );
+      this.eventBus.emit(new BuildUnitIntentEvent(buildableUnit.type, tile));
     }
     this.hideMenu();
   }