Fix chunked encoding with broken ending

[algesten]

Some websites do not end chunked encoding correctly. The spec says the end should be:

0\r\n
\r\n

However some sites stop short after 0\r\n. Curl handles this case fine.

Close #325

[algesten]

I don't actually have a plan for how to fix this just yet.

I don't know whether the people behind the chunked_transfer crate would be open to a fix where the final \r\n is optional. Otherwise we need to handle it un ureq.

[Shnatsel]

This needs to be handled with care, since it might allow HTTP desync attacks and request smuggling.

@jhwgh1968 might know more about this particular case.

[algesten]

@Shnatsel Good point! I provided a naive fix in upstream repo – maybe needs more thought. 🤔 frewsxcv/rust-chunked-transfer#11

[jsha]

I comment on #325 (comment) - I think we should first implement trailers and see if we still have this problem. At least one of the affected sites that I spot-checked was actually sending trailers.