recent_topics: Don't mark messages as read on scrolling.

throttled mousewheel handler marks messages as read in the
message_list regardless of if the message_list is visible or not.

We don't trigger it if recent_topics is visible.

static/js/ui_init.js

@@ -91,7 +91,7 @@ exports.initialize_kitchen_sink_stuff = function () {
 
     message_viewport.message_pane.on("wheel", (e) => {
         const delta = e.originalEvent.deltaY;
-        if (!overlays.is_active()) {
+        if (!overlays.is_active() && !recent_topics.is_visible()) {
             // In the message view, we use a throttled mousewheel handler.
             throttled_mousewheelhandler(e, delta);
         }