Fix #1537: don't access elements of empty vector
m_accessUnitPicInfo may be empty in DecLib::checkLayerIdIncludedInCvss()when the bitstream ends after skipping pictures. m_accessUnitPicInfo.begin() is undefined in that case.
m_accessUnitPicInfo may be empty in DecLib::checkLayerIdIncludedInCvss()when the bitstream ends after skipping pictures. m_accessUnitPicInfo.begin() is undefined in that case.