CoverBrowser: fix no content with Pathchooser in RTL UI

Really needed these :resetLayout() (as done in Menu.lua)
when stuff is right aligned (otherwise, first computation
of x-offset, when there was no content, being Screen.width,
would stick, and would draw the content off-screen on the
right - no issue noticed when left-aligned as the offsets
would stay being 0 whether there is content or none).

plugins/coverbrowser.koplugin/covermenu.lua

@@ -50,6 +50,8 @@ function CoverMenu:updateItems(select_number)
     self:_recalculateDimen()
     self.page_info:resetLayout()
     self.return_button:resetLayout()
+    self.vertical_span:clear()
+    self.content_group:resetLayout()
     -- default to select the first item
     if not select_number then
         select_number = 1