Buffered WPXSvInputStream

Change-Id: I8bb2632cb018093d02e21090e77bb48364f99268
Reviewed-on: https://gerrit.libreoffice.org/7146
Reviewed-by: David Tardon <dtardon@redhat.com>
Tested-by: David Tardon <dtardon@redhat.com>
(cherry picked from commit c56c2e28ff4252aa858826416a8a57cb8c2bf100)

Simplify this condition a bit

Change-Id: Iceef995be9ff55306550e56a0be87dddab7a78c3
(cherry picked from commit c85456b01bd8dd12792b76fb393f893496461c5c)

Avoid some memcpy when not necessary

Change-Id: I9b838fc8392bc61be4ed911fb1423a1e97af2356
(cherry picked from commit 4b4a870b176cf5ff9ee84fc5b16f4df1d8eeef94)
Reviewed-on: https://gerrit.libreoffice.org/7279
Reviewed-by: Michael Meeks <michael.meeks@collabora.com>
Tested-by: Michael Meeks <michael.meeks@collabora.com>