When the sheet name/cell address separator was an exclamation mark,
bad conversion of the optional dot separator replaced the last dot
of the exported sheet name, resulting broken links:

'sheet.name.with!dot'!A1

Change-Id: I84fb6c8da345c144b04657ea350f1f96614071b7
Reviewed-on: https://gerrit.libreoffice.org/69272
Tested-by: Jenkins
Reviewed-by: László Németh <nemeth@numbertext.org>