Fix warning from compilers where sizeof(size_t) > sizeof(int)
Fix warning from compilers where sizeof(size_t) > sizeof(int)

Without this fix, a bunch of warnings are spewed

Signed-off-by: Dave Thaler <8a98d0850f57b73c42d096f8f8b11e2d5522d554@ntdev.microsoft.com>

ytakano/radix_tree