As the crash tests have shown, the assert introduced with
71b630e5 to force verification of the
assumption made in 8e2293e0 was hit in
120 documents.

Citing from https://gerrit.libreoffice.org/#/c/14427/ comment:
"The assumptions behind this patch are wrong. This only works if every
single part of the export goes through StartRecord/EndRecord calls. We
have some features that don't use that and need the STREAM_SEEK_TO_END
in the beginning of the StartRecord."

Revert "replace an OSL_ENSURE() with assert(), tdf#89319 related"

This reverts commit 71b630e5.

Revert "tdf#89319 remove redundant file seekings in XLS export"

This reverts commit 8e2293e0.