The graph lookup is suprisingly costly and so is
filtering. By specializing the lookup with filtering
the logic is more readable and slightly faster (~35%
in debug build).

Change-Id: Id35a562c76a84a81362f47b61ed67fb74d0a6dc7
Reviewed-on: https://gerrit.libreoffice.org/63001
Tested-by: Jenkins
Reviewed-by: Ashod Nakashian <ashnakash@gmail.com>