http: set content length earlier

[jay]

• Make content length (ie download size) accessible to the user in the
  header callback, but only after all headers have been processed (ie
  only in the final call to the header callback).

Background:

For a long time the content length could be retrieved in the header
callback via CURLINFO_CONTENT_LENGTH_DOWNLOAD_T as soon as it was parsed
by curl.

Changes were made in 8a16e54 (precedes 7.79.0) to ignore content length
if any transfer encoding is used. A side effect of that was that
content length was not set by libcurl until after the header callback
was called the final time, because until all headers are processed it
cannot be determined if content length is valid.

This change keeps the same intention --all headers must be processed--
but now the content length is available before the final call to the
header function that indicates all headers have been processed (ie
a blank header).

Bug: 8a16e54#r57374914
Reported-by: sergio-nsk@users.noreply.github.com

Fixes #7804
Closes #xxxx

[jay]

changed it to deduplicate a separate similar check that occurs after all headers have been received

[jay]

some hyper tests for maximum filesize are failing so I have to look into that. the other CI failures don't make sense, they are all ignored tests but fail anyway, for example this one:

2021-10-01T19:53:57.7418818Z TESTDONE: 1171 tests out of 1174 reported OK: 99%
2021-10-01T19:53:57.7419127Z 
2021-10-01T19:53:57.7419716Z TESTFAIL: These test cases failed: (203) (1056) (1143) 
2021-10-01T19:53:57.7420845Z 
2021-10-01T19:53:57.7462698Z make[1]: *** [nonflaky-test] Error 1
2021-10-01T19:53:57.7465251Z make[1]: Leaving directory `/c/__w/1/s/tests'
2021-10-01T19:53:57.7559396Z make: *** [test-nonflaky] Error 2
2021-10-01T19:53:57.8742529Z ##[error]Cmd.exe exited with code '2'. 

[bagder]

2021-10-01T19:53:57.7419716Z TESTFAIL: These test cases failed: (203) (1056) (1143)

That certainly looks like a test script bug!

[bagder]

@jay I believe my fixup addressed the remaining issue. Anything left or should this get merged?

[jay]

Thanks, that seems to have done it. I've squashed it, rebased on master and will wait for another round of CI results.

[jay]

All of the failures look like random flakiness, however one of them in windows msys1_mingw32_debug was test 566 which is content length related, so I'm rerunning that CI until it passes.