linguistic/workben/sspellimp.cxx fix cppcheck error

Change-Id: I5727b254126b23d98fb94068a6254c9ee0e13eba
Reviewed-on: https://gerrit.libreoffice.org/10701
Reviewed-by: Joren De Cuyper <jorendc@libreoffice.org>
Tested-by: Joren De Cuyper <jorendc@libreoffice.org>