SAST: coverity scan : Operands don't affect result

[raghvendra-dixit]

As part of coverity scan , following is observed in Details: The expression's value does not depend on the operands; often, this represents an inadvertent logic error. In github.​com/ugorji/go/codec.​mpdesc(byte, string): An operation with non-constant operands that computes a result with constant value.