Synchornize unread marker when other client opens a channel

Fixes #863

client/js/socket-events/open.js

@@ -3,9 +3,27 @@
 const $ = require("jquery");
 const socket = require("../socket");
 
+// Sync unread badge and marker when other clients open a channel
 socket.on("open", function(id) {
-	// Another client opened the channel, clear the unread counter
+	if (id < 1) {
+		return;
+	}
+
+	const channel = $("#chat #chan-" + id);
+
+	// Don't do anything if the channel is active on this client
+	if (channel.length === 0 || channel.hasClass("active")) {
+		return;
+	}
+
+	// Clear the unread badge
 	$("#sidebar").find(".chan[data-id='" + id + "'] .badge")
 		.removeClass("highlight")
 		.empty();
+
+	// Move unread marker to the bottom
+	channel
+		.find(".unread-marker")
+		.data("unread-id", 0)
+		.appendTo(channel.find(".messages"));
 });