trivial level 4 warnings on ms vs_142, cpp2017

[vacazboara]

I'd suggest fixing:
..\cpp-httplib\httplib.h(1518,45): warning C4100: 'ifn': unreferenced formal parameter
and
..\cpp-httplib\httplib.h(2852,65): warning C4458: declaration of 'status' hides class member

Thanks

[yhirose]

@vacazboara, thanks for the report!

[vacazboara]

wow, that was fast! thanks!