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

Commit 8e2293e06adba3f22e824acad99983fb5b997e4d changed
STREAM_SEEK_TO_END logic, ensure that in a dbgutil build we catch
unnoticed corner cases with assert() instead of just another fly-by
warning.

Change-Id: If6c4fb4d2467f7dc7b8177caf7353d0b0e56ed0d

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core