wxArtProvider::GetIconBundle() cleanup:

wxArtProvider::GetIconBundle() cleanup:
* makes GetIcon() and GetBitmap() behave in the same way again (i.e. GetBitmap
  falls back to CreateIconBundle too)
* GetIcon() used to call CreateIconBundle() first, before CreateBitmap() - this
  doesn't make sense, inverted
* GetIconBundle() falls back to GetIcon() if provider's CreateIconBundle()
  doesn't return anything and vice versa: GetIcon()/GetBitmap() falls back to
  GetIconBundle() if CreateBitmap() doesn't return anything

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@59930 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775