[Form][2.3] Fixes empty file-inputs getting treated as extra field.
bug #10251 [Form][2.3] Fixes empty file-inputs getting treated as extra field. (jenkoian)

This PR was squashed before being merged into the 2.3 branch (closes #10251).

Discussion
----------

[Form][2.3] Fixes empty file-inputs getting treated as extra field.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #8575 (https://github.com/symfony/symfony/pull/8575#issuecomment-34867485)
| License       | MIT

Re-applies 968fe23 (PR #8575).

The test for this already exists, it was just this line that got overwritten by https://github.com/symfony/symfony/commit/eb9f76d5bad120c1d4b3b30c2d8c73bb9d5928e8#diff-ca5e25b47f3ecc94cd557946aeb486c6L542

To clarify, this is a PR into 2.3 branch - this already exists in 2.4 (and later from this PR: https://github.com/symfony/symfony/pull/9146)

Commits
-------

8d99d75 [Form][2.3] Fixes empty file-inputs getting treated as extra field.
Add tests for RequestStack class
minor #10326 [HttpFoundation][Tests] Add tests for RequestStack class (inalgnu)

This PR was submitted for the 2.3-dev branch but it was merged into the 2.3 branch instead (closes #10326).

Discussion
----------

[HttpFoundation][Tests] Add tests for RequestStack class

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

Commits
-------

6f25d39 [HttpFoundation][Tests] Add tests for RequestStack class
[HttpKernel] fixed CS
[HttpFoundation] removed test file not related to 2.3
minor #10372 [HttpKernel] fixed CS (fabpot)

This PR was merged into the 2.3 branch.

Discussion
----------

[HttpKernel] fixed CS

Commits
-------

7539e41 [HttpKernel] fixed CS