PopupMenu::addSeparator() after addSectionHeader()

Currently, the PopupMenu class is smart enough not to actually add a separator if addSeparator() is called twice or when the menu is still empty.

But if the menu just contains a section header added with addSectionHeader(), the separator is added even if it can be argued that it’s not really necessary.

Below is a suggested improvement that allows skipping the addition of a separator when in happens after a section header.
There is no way to do this via client code because it’s not possible to get the last item in a popup menu.

/* argument added with default value that avoids breaking change */
void PopupMenu::addSeparator(const bool skipAfterSectionHeader = false)
    if (items.size() > 0 
        && ! items.getLast().isSeparator
        && (! skipAfterSectionHeader || ! items.getLast().isSectionHeader)) //< proposed change
        Item i;
        i.isSeparator = true;
        addItem (std::move (i));