Update http_foundation.rst

`$request->query->all()['foo'];` triggers an 'Undefined array key "foo"' error when `foo` doesn't exist. However `$request->query->all('foo');` return null  when `foo` doesn't exist (consistent with `$request->query->get('bar');` for accessing a string parameter `bar` which might not exist).

Author: jontjs

components/http_foundation.rst

@@ -169,7 +169,7 @@ doesn't support returning arrays, so you need to use the following code::
     // the query string is '?foo[bar]=baz'
 
     // don't use $request->query->get('foo'); use the following instead:
-    $request->query->all()['foo'];
+    $request->query->all('foo');
     // returns ['bar' => 'baz']
 
     $request->query->get('foo[bar]');