Handle CHATHISTORY messages when reaching end of batch

Closes: https://todo.sr.ht/~emersion/gamja/115

lib/client.js

@@ -886,7 +886,7 @@ export default class Client extends EventTarget {
 		let max = Math.min(limit, this.isupport.chatHistory());
 		let params = ["BEFORE", target, "timestamp=" + before, max];
 		return this.roundtripChatHistory(params).then((messages) => {
-			return { more: messages.length >= max };
+			return { messages, more: messages.length >= max };
 		});
 	}
 
@@ -904,7 +904,7 @@ export default class Client extends EventTarget {
 				after.time = messages[messages.length - 1].tags.time;
 				return this.fetchHistoryBetween(target, after, before, limit);
 			}
-			return null;
+			return { messages };
 		});
 	}