Close join error (#3454)

## Description:

When joining a game after it fills up, the server rejects the player
join and the player leaves the lobby, but the join modal stays up.

## 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

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

evan

src/client/components/BaseModal.ts

@@ -35,6 +35,10 @@ export abstract class BaseModal extends LitElement {
     return this;
   }
 
+  public isOpen(): boolean {
+    return this.isModalOpen;
+  }
+
   protected firstUpdated(): void {
     if (this.modalEl) {
       this.modalEl.onClose = () => {