xmlIO: Fix reading from non-regular files like pipes Commit 7e14c05d removed unnecessary copying of uncompressed input through zlib or xzlib. This broke input from non-regular files like pipes which can't be reopened. Try to detect such files by checking whether they're seekable and always pipe them through zlib or xzlib. Also remove seemingly unnecessary calls to gzread and gzrewind to support unseekable files. Fixes https://gitlab.gnome.org/GNOME/libxslt/-/issues/124.