The problem was that in case the document has shapes where the order
does not match the z-index order, so sorting is needed, then sorting
failed to take the multi-image feature into account. E.g. SVG images
have a PNG fallback, but at the end of the shape import the PNG
fallback is removed, which means the "actual" (not the "wished") z-index
of the shapes after the SVG image has to be adjusted.

Without this happening SvxDrawPage::getByIndex() (or in case of Writer,
SwTextBoxHelper::getByIndex()) will throw when the importer calls
getByIndex(3) but we only have 3 shapes. This results in not honoring
the z-index request of the remaining shapes.

Regression from commit 44cfc7cb (re-base
on ALv2 code. Includes (at least) relevant parts of:, 2012-10-09), from
the

        Svg: Reintegrated Svg replacement from /branches/alg/svgreplavement
        http://svn.apache.org/viewvc?view=revision&revision=1220836

part.

Change-Id: Ibe880e5c6c74b728b4a760498720ee31f052b726
Reviewed-on: https://gerrit.libreoffice.org/36998Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins <ci@libreoffice.org>