fix #40: httpsys crashes node.exe when serving static files

[gimelfarb]

Fixing an issue where httpsys native module crashes node.exe process with Access Violation 0xc0000005, when responding to a request for a static file (or any large response).

Also adding a unit test which replicates the issue, and tests that it is fixed.

[gimelfarb]

I have added the explanation of the fix in the comment for the issue #40 .