ui_util: Stop propagation enter keypress when it is already handled.

This is good to do in general for these type of event handlers
and this also fixes a bug where pressing on reply button in
the recent topics will open compose with a new line since
browser assumed enter was pressed on compose_textarea since
process_enter_key returned false.

static/js/ui_util.js

@@ -35,6 +35,8 @@ export function convert_enter_to_click(e) {
     const key = e.which;
     if (key === 13) {
         // Enter
+        e.preventDefault();
+        e.stopPropagation();
         $(e.currentTarget).trigger("click");
     }
 }