fdo#37326: Sign number must be either 1 or -1, never 0.
fdo#37326: Sign number must be either 1 or -1, never 0.

This fixes incorrect result with LINEST cell function.

Signed-off-by: Kohei Yoshida <9e4d5b032dac9356f08b4c568a6a5bfefe761338@novell.com>

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