Workaround for streams with size > SAL_MAX_INT32.

More complicated ways using available() and navigating cross-thread
are possible, but probably harder to maintain.

Change-Id: I721b1f38055dfcea03fef555b8a5fd93dfc1b886
Reviewed-on: https://gerrit.libreoffice.org/39374Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Meeks <michael.meeks@collabora.com>