Fixes a regression from commit:
f675cfe90f
It is not sufficient to only check if the builder is empty, as we will
then drop empty header values (when the first found value is empty).
This is tested in WPT by /cors/origin.htm, but that requires an HTTP
server.
According to RFC 2046, the BNF of the form data body is:
multipart-body := [preamble CRLF]
dash-boundary transport-padding CRLF
body-part *encapsulation
close-delimiter transport-padding
[CRLF epilogue]
Where "epilogue" is any text that "may be ignored or discarded". So we
should stop parsing the body once we encounter the terminating delimiter
("--").
Note that our parsing function is from an attempt to standardize the
grammar in the spec: https://andreubotella.github.io/multipart-form-data
This proposal hasn't been updated in ~4 years, and the fetch spec still
does not have a formal definition of the body string.
This patch ensure Headers object's associated header list
is ISO-8859-1 encoded when set using `Infra::isomorphic_encode`,
and correctly decoded using `Infra::isomorphic_decode`.
Follow-up of https://github.com/LadybirdBrowser/ladybird/pull/1893
The events tested here are decidedly async. We also can't really write
sync tests of the form "test(async () => {})". Nothing will await the
async callback.
