This centralizes the code that handles templates, and allows the empty files to use default templates. This partially reverts commits:ada07f303eAuthor Miklos Vajna <vmiklos@collabora.com> Date Wed Oct 28 14:54:52 2020 +0100 tdf#123476 filter: try to detect 0-byte files based on extension2854362f42Author Mike Kaganski <mike.kaganski@collabora.com> Date Wed Jan 27 16:05:54 2021 +0100 tdf#123476 filter: Also handle empty ODFdff586735bAuthor Mike Kaganski <mike.kaganski@collabora.com> Date Mon May 03 17:04:04 2021 +0200 tdf#123476: also use filter by extension when its service is the same The unit tests from these commits are retained and extended for templates. Change-Id: I755738d2d5a6d6955d84d6e12f3accc017e0391f Reviewed-on: https://gerrit.libreoffice.org/c/core/+/132938 Tested-by: Jenkins Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>