Fix FormHelper::create() dropping 0 value parameter.

When 0 is the first passed parameter we shouldn't drop it.

Fixes #6107

lib/Cake/Test/Case/View/Helper/FormHelperTest.php

@@ -8642,6 +8642,7 @@ class FormHelperTest extends CakeTestCase {
 			'escape' => false,
 			'url' => array(
 				'action' => 'edit',
+				'0',
 				'myparam'
 			)
 		));
@@ -8649,7 +8650,7 @@ class FormHelperTest extends CakeTestCase {
 			'form' => array(
 				'id' => 'ContactAddForm',
 				'method' => 'post',
-				'action' => '/contacts/edit/myparam',
+				'action' => '/contacts/edit/0/myparam',
 				'accept-charset' => $encoding
 			),
 			'div' => array('style' => 'display:none;'),
@@ -8667,8 +8668,8 @@ class FormHelperTest extends CakeTestCase {
 	public function testCreateNoErrorsWithMockModel() {
 		$encoding = strtolower(Configure::read('App.encoding'));
 		$ContactMock = $this->getMockBuilder('Contact')
-				->disableOriginalConstructor()
-				->getMock();
+			->disableOriginalConstructor()
+			->getMock();
 		ClassRegistry::removeObject('Contact');
 		ClassRegistry::addObject('Contact', $ContactMock);
 		$result = $this->Form->create('Contact', array('type' => 'GET'));

lib/Cake/View/Helper/FormHelper.php

@@ -408,7 +408,7 @@ class FormHelper extends AppHelper {
 				'action' => $options['action'],
 			);
 			$options['action'] = array_merge($actionDefaults, (array)$options['url']);
-			if (empty($options['action'][0]) && !empty($id)) {
+			if (!isset($options['action'][0]) && !empty($id)) {
 				$options['action'][0] = $id;
 			}
 		} elseif (is_string($options['url'])) {