fdo#39135: Prevent integer overflow & update the character during loop.
fdo#39135: Prevent integer overflow & update the character during loop.

These two errors in the code contributed to the reported bug.  Let's
fix them.

Change-Id: If82a1bd4d1e27145b48e722b30388cc9dc4a8a6e

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