fdo#48065 SVG: correctly clamp fill-opacity

See W3 test http://www.w3.org/Graphics/SVG/Test/20061213/htmlObjectHarness/full-painting-fill-05-b.html
which is also attached to the bug document.
This fixes the behavior of the insert > image > from file behavior.
The open behavior is already fixed by 79a6e40e6f19a896dbc25640deb3d4507eddad95

Change-Id: I9e3a3755bac25ca596d418c229a78cb23e07d3f3
Reviewed-on: https://gerrit.libreoffice.org/10523
Reviewed-by: David Tardon <dtardon@redhat.com>
Tested-by: David Tardon <dtardon@redhat.com>