cppcheck: fix same expression, check once !mxTable.is()
cppcheck: fix same expression, check once !mxTable.is()

Change-Id: Ie12146f3c2f18c5ec9a49a666f327772493fcf03

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