Fix multiple selects always failing post validation.

Fixes #3218

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

@@ -4256,6 +4256,23 @@ class FormHelperTest extends CakeTestCase {
 	}
 
 /**
+ * Multiple select elements should always be secured as they always participate
+ * in the POST data.
+ *
+ * @return void
+ */
+	public function testSelectMultipleSecureWithNoOptions() {
+		$this->Form->request['_Token'] = array('key' => 'testkey');
+		$this->assertEquals(array(), $this->Form->fields);
+
+		$result = $this->Form->select(
+			'Model.select',
+			array(),
+			array('multiple' => true)
+		);
+		$this->assertEquals(array('Model.select'), $this->Form->fields);
+	}
+/**
  * When a select box has no options it should not be added to the fields list
  * as it always fail post validation.
  *

lib/Cake/View/Helper/FormHelper.php

@@ -1850,10 +1850,12 @@ class FormHelper extends AppHelper {
 
 		if (!empty($tag) || isset($template)) {
 			$hasOptions = (count($options) > 0 || $showEmpty);
+			// Secure the field if there are options, or its a multi select.
+			// Single selects with no options don't submit, but multiselects do.
 			if (
 				(!isset($secure) || $secure == true) &&
 				empty($attributes['disabled']) &&
-				$hasOptions
+				(!empty($attributes['multiple']) || $hasOptions)
 			) {
 				$this->_secure(true);
 			}