Git Bug Report: git credential 'url' parsing clear other fields

Hi,

I encountered what seems to be a small bug in git credential parsing. Just want to confirm it's not expected behavior. I'm willing to work on a patch.

First time submitting a bug to git (and a potential patch), so let me know if I do anything wrong!

What did you do before the bug happened? (Steps to reproduce your issue)

Run git credential approve with the 'url' field of the form NOT as first entry.

example: git -c credential.helper= -c "credential.helper=store --file=.git-credentials" credential approve

input: ``` username=user password=s3cret url=https://example.com/repository.git ```

This next input works as intended. input: ``` url=https://example.com/repository.git username=user password=s3cret ```

This was reproduced on both master and next branches.

What did you expect to happen? (Expected behavior)

Credentials should be saved with `username` and `password` provided. `url` parsing should not clear the `credential` struct.

What happened instead? (Actual behavior)

`username` and `password` are correctly parsed and stored in the struct. `url` parsing then clear the fields.

Culprit would be this `credential_clear` in `credential_from_url_1`. On branch `next`, commit `2a3ae87e7f8e9585d7565a8b5d6a6c9c28d6d943`.

Thanks, Thomas Desveaux