[BUG] PopupMenu::ItemComponent ignores custom components for section headers

ItemComponent ignores custom components for section headers. Adding a test for whether customComp is nullptr would prevent this from happening in cases where a custom component has already been provided. Users wouldn’t be able to inherit from HeaderItemComponent but a custom section header would still be simple enough to implement.

This is also helpful because there’s not a way to resize the section header independently from normal items. (getIdealPopupMenuItemSize only has a flag for whether the item is a separator – it’d be great to have an enum instead or separate methods, but that’d be a bigger breaking change.)

      ItemComponent (const PopupMenu::Item& i, int standardItemHeight, MenuWindow& parent)
     : item (i), customComp (i.customComponent)
       if (item.isSectionHeader) // change to (item.isSectionHeader && customComp == nullptr)
           customComp = *new HeaderItemComponent (item.text);

       if (customComp != nullptr)
           setItem (*customComp, &item);
           addAndMakeVisible (*customComp);

       parent.addAndMakeVisible (this);


       int itemW = 80;
       int itemH = 16;
       getIdealSize (itemW, itemH, standardItemHeight);
       setSize (itemW, jlimit (1, 600, itemH));

       addMouseListener (&parent, false);