uiIntraPeriod is unsigned, and thus can't ever be negative.
The subtraction on the line above can't ever make the value wrap
around either, since param_.uiIntraPeriod % uiGOPSize always is
smaller than or equal to param_.uiIntraPeriod. Thus, the check
never is necessary even if the value would be signed either.
This fixes warnings when building with clang.