tdf#119050 sfx2 store: don't inherit temp file permissions when overwriting

tdf#119050 sfx2 store: don't inherit temp file permissions when overwriting

The too aggressive error handling in commit
fb04780cf8523ad4e900ae8b9cecbe7a2697a12a (tdf#116117 sfx2 store: don't
inherit temp file permissions when renaming, 2018-03-12) means that if
the file is already there, then we don't try to stat() it; even if there
is no problem with that.

(cherry picked from commit 38afe2976eea427999c39ee3a73e7938ec8d5f7b)

Change-Id: Ie0b9084064834e339bcae3ad7b4a35c54cb9d3c2
Reviewed-on: https://gerrit.libreoffice.org/59709
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>
Gbp-Pq: Name do-not-reset-permissions-on-save.diff