args.c: fix range check in int/uint

this also clears the remaining -Wshorten-64-to-32 warnings in this file.
the previous patch ported from libvpx was incomplete due to:
d3a7576fb Add compiler flag -Wsign-compare

Change-Id: I105fa2342073dfa8bd0619b4282435fb6568f5c9
1 file changed