[PATCH] content_encoding: brotli and others, pass through 0-length writes

[PATCH] content_encoding: brotli and others, pass through 0-length writes

- curl's transfer handling may write 0-length chunks at the end of the
  download with an EOS flag. (HTTP/2 does this commonly)

- content encoders need to pass-through such a write and not count this
  as error in case they are finished decoding

Fixes #13209
Fixes #13212
Closes #13219

Gbp-Pq: Name content_encoding_brotli_and_others_pass_through_0_length_writes.patch