vcl: typo in variable name in PaintLineGeometryWithEvtlExpand

Change-Id: I87084cbc4d6a8b6f5edbf8b90791c2b1e75b4afb
Reviewed-on: https://gerrit.libreoffice.org/12211
Reviewed-by: Chris Sherlock <chris.sherlock79@gmail.com>
Tested-by: Chris Sherlock <chris.sherlock79@gmail.com>