bnc#865381 DOCX import: fix w:trHeight for cells with btLr text direction

Also extend testcase: I made sure that the new version fails without
this fix and without the fix from
48b5b7641d0df960558082e8948da8598f801264 as well.

Change-Id: If33aa6d33cdc287620c12b84ad3f50279568bc8d