Fix #722 on encoder crash for YUV444 coding

Fix the crash while keeping UseIdentityTableForNon420Chroma. The patch was provided by Philippe (Philippe.DeLagrange@InterDigital.com)

merged

mentioned in commit 44cb3264

Thanks ! Looks just fine. Feel free to add attached patch for software-manual.tex (typo fixes: Cr instead of Cb and double 'that')doc.patch