fdo#43534: Reset tab index for SingleRefToVars() call.
fdo#43534: Reset tab index for SingleRefToVars() call.

Otherwise that method will set #REF! to the cell when it sees the tab
index being -1.  We don't use that index in that code, so it's safe to
do this.

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