Make code flow clearer in WinHttpUrlFetcher.

In BuildRequestAndFetchResultFromHttpService(), instead of using `hr` to
keep track of the result, and breaking out of a for-loop, just return
the result as soon as its known.

Change-Id: Ide6043e748a2ad31a68f02cc84eaaf2e4e3f1c66
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3378845


Reviewed-by: Roger Tawa <rogerta@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/main@{#958210}