fix: Allow events without parameters

[susnux]

Currently emit requires two parameters even if the event type is set to undefined. So emit('foo') will cause a Typescript error.

This fixes it by removing the second argument if the event type is set to undefined.

---

common:

declare module '@nextcloud/event-bus' {
	export interface NextcloudEvents {
		// mapping of 'event name' => 'event type'
		'my:event': undefined
	}
}

before:

emit('my:event', undefined)

after

emit('my:event')