Nested navigation dropdowns don't work on small screens (mobile view)

This bug appeared after update from 2.8 to 2.9
Scenario:

1. Choose moodle clean theme
2. Set the top navigation menu to the suggested setting - this would include nested menus
   e.g.

   Moodle community|https://moodle.org

   -Moodle development|https://moodle.org/development

   --Moodle Docs|http://docs.moodle.org|Moodle Docs

   ---Moodle level 3|http://google.com

   ---Moodle level 34|http://google.com

   ---Moodle level 3|http://google.com

   --Moodle 22Docs|http://docs.moodle.org|Moodle Docs

   ---Moodle level 3|http://google.com

   ---Moodle level 34|http://google.com

   ---Moodle level 3|http://google.com

   --German Moodle Docs|http://docs.moodle.org

   -Moodle development|https://moodle.org/development

   --Moodle Docs|http://docs.moodle.org|Moodle Docs

   ---Moodle level 3|http://google.com

   ---Moodle level 34|http://google.com

   ---Moodle level 3|http://google.com

   --Moodle 22Docs|http://docs.moodle.org|Moodle Docs

   ---Moodle level 3|http://google.com

   ---Moodle level 34|http://google.com

   ---Moodle level 3|http://google.com

   --German Moodle Docs|http://docs.moodle.org

3. resize the window so that the navagation menu gets in mobile view
4. try to open any of the nested submenus - all the menus are closing

What I expected - nested dropdown menus to work in mobile view
What actually happens - instead of opening a submenu, the top-level menus are get closed

This happens due to a bug in the bootstrapbase javascript - in theme/bootstrapbase/amd/src/bootstrap.js, lines 667-748. The function clearMenus() is called everytime a dropdown is toggled, and it causes all the menus to be closed.

Here is a patch that fixes the bug with a few small changes:

diff --git a/theme/bootstrapbase/amd/src/bootstrap.js b/theme/bootstrapbase/amd/src/bootstrap.js

index 196975e..35fb020 100644

--- a/theme/bootstrapbase/amd/src/bootstrap.js

+++ b/theme/bootstrapbase/amd/src/bootstrap.js

@@ -679,15 +679,15 @@ define(['jquery'], function($) {

       isActive = $parent.hasClass('open')

-      clearMenus()

+      clearMenus($this)

       if (!isActive) {

         if ('ontouchstart' in document.documentElement) {

           // if mobile we we use a backdrop because click events don't delegate

           $('<div class="dropdown-backdrop"/>').insertBefore($(this)).on('click', clearMenus)

         }

-        $parent.toggleClass('open')

       }

+      $parent.toggleClass('open')

       $this.focus()

@@ -737,10 +737,13 @@ define(['jquery'], function($) {

   }

-  function clearMenus() {

+  function clearMenus($e) {

     $('.dropdown-backdrop').remove()

     $(toggle).each(function () {

-      getParent($(this)).removeClass('open')

+      var $parent = getParent($(this))

+      if ($e == undefined || $parent.find($e).length == 0) {

+          $parent.removeClass('open')

+      }

     })

   }