fix: room creation error handling

fix #14

ts/Manager/App.tsx

@@ -63,10 +63,10 @@ const App: React.FC<Props> = () => {
 
 	function addRoom(name: string) {
 		if (!name) {
-			return;
+			return Promise.resolve();
 		}
 
-		api.createRoom(name).then(room => {
+		return api.createRoom(name).then(room => {
 			setRooms(rooms.concat([room]));
 		});
 	}

ts/Manager/NewRoomForm.tsx

@@ -1,29 +1,41 @@
 import React, { useState } from 'react';
 
 type Props = {
-    addRoom: (name: string) => void;
+	addRoom: (name: string) => Promise<void>;
 }
 
 const NewRoomForm: React.FC<Props> = (props) => {
-	const [name, setName] = useState('');
+	const [name, setName] = useState<string>('');
+	const [processing, setProcessing] = useState<boolean>(false);
+	const [error, setError] = useState<string>('');
 
 	function addRoom(ev: React.FormEvent) {
 		ev.preventDefault();
 
-		props.addRoom(name);
+		setProcessing(true);
+		setError('');
 
+		props.addRoom(name).then(() => {
 			setName('');
+		}).catch(err => {
+			setError(err.toString());
+		}).then(() => {
+			setProcessing(false);
+		});
 	}
 
 	return (
 		<form action="#" onSubmit={addRoom}>
 			<input
 				className="newgroup-name"
+				disabled={processing}
 				value={name}
 				placeholder={t('bbb', 'Room name')}
 				onChange={(event) => { setName(event.target.value); }} />
 
-			<input type="submit" value={t('bbb', 'Create')} />
+			<input type="submit" disabled={processing} value={t('bbb', 'Create')} />
+
+			{error && <p>{error}</p>}
 		</form>
 	);
 };