...for one, this avoids sending seek requests down the GIO/GVFS stack, which can
silently fail with corrupt data read from certain broken servers for current
versions of the GIO/GVFS stack; for another, it should considerably speed up
loading documents via the GIO UCP, as LO's document type detection is notorious
for issuing lots of seek and (small-chunk and/or re-) read operations on a file.

(This issue has become more relevant after
51e0d789 "rhbz#1134285: Access dav, davs URLs
via GVFS," where the old route via the WebDAV UCP was apparently not affected by
those broken servers, so happened to start affecting opening certain remote
files in LO via Nautilus.)

Change-Id: I91f91128b2d1a16f976eafeacf216a91747f4df1
(cherry picked from commit 93a0696e)
Reviewed-on: https://gerrit.libreoffice.org/18612Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>