[HttpFoundation] getClientIp is fixed.

	| Q             | A
	| ------------- | ---
	| Bug fix?      | yes
	| New feature?  | no
	| BC breaks?    | no
	| Deprecations? | no
	| Tests pass?   | yes
	| Fixed tickets | n/a
	| License       | MIT
	| Doc PR        | no

The getClientIp now returns ip of the earliest server in a proxy chain when all the servers in the chain are trusted proxies. Before this patch the getClientIp used to return null at such condition.
Some appropriate tests are added.