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

Author: jenkoian

src/Symfony/Component/Form/Form.php

@@ -556,7 +556,7 @@ public function submit($submittedData, $clearMissing = true)
                 }
 
                 foreach ($this->children as $name => $child) {
-                    if (isset($submittedData[$name]) || $clearMissing) {
+                    if (array_key_exists($name, $submittedData) || $clearMissing) {
                         $child->submit(isset($submittedData[$name]) ? $submittedData[$name] : null, $clearMissing);
                         unset($submittedData[$name]);
 

src/Symfony/Component/Form/Tests/CompoundFormTest.php

@@ -115,7 +115,7 @@ public function testSubmitDoesNotAddExtraFieldForNullValues()
         $child = $factory->create('file', null, array('auto_initialize' => false));
 
         $this->form->add($child);
-        $this->form->submit(array('file' => null));
+        $this->form->submit(array('file' => null), false);
 
         $this->assertCount(0, $this->form->getExtraData());
     }