Set #VALUE! error in COVAR() OpenCL implementation when appropriate
Set #VALUE! error in COVAR() OpenCL implementation when appropriate

Returning -DBL_MAX doesn't make sense. The traditional C++ implementation and
other spreadsheet products return an error.

Change-Id: I71117c0b1f113d31ad6eb0c1798b74f96b3a75de

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