msac: Add a cast to indicate intended narrowing from size_t to unsigned
This fixes this compiler warning with MSVC:
../src/msac.c(148): warning C4267: '+=': conversion from 'size_t' to 'unsigned int', possible loss of dataThis fixes this compiler warning with MSVC:
../src/msac.c(148): warning C4267: '+=': conversion from 'size_t' to 'unsigned int', possible loss of dataVideoLAN code repository instance