[messaging-core][ios] getCurrentToken stalls

[PeterStaev]

The problem is in this code:

firebase/packages/firebase-messaging-core/index.ios.ts

Lines 156 to 159 in 5b7be94

	if ((await this.hasPermission()) === AuthorizationStatus.DENIED) {
	reject(new Error('Device is unauthorized to receive an APNSToken token.'));
	return;
	}

The problem happens in cases where the permission check executes before the call of the _onToken callback. This leaves the promise dangling and the function never completes.