Do not validate widgets that do not submit input (see contao#2261)

Description
-----------

| Q                | A
| -----------------| ---
| Fixed issues     | Fixes contao#2210
| Docs PR or issue | -

Commits
-------

2f83d0a Do not validate widgets that do not submit input

core-bundle/src/Resources/contao/classes/DataContainer.php

@@ -373,7 +373,7 @@ protected function row($strPalette=null)
 			}
 
 			// Validate and save the field
-			if (\in_array($this->strInputName, $paletteFields) || Input::get('act') == 'overrideAll')
+			if ($objWidget->submitInput() && (\in_array($this->strInputName, $paletteFields) || Input::get('act') == 'overrideAll'))
 			{
 				$objWidget->validate();
 
@@ -385,7 +385,7 @@ protected function row($strPalette=null)
 						$this->noReload = true;
 					}
 				}
-				elseif ($objWidget->submitInput())
+				else
 				{
 					$varValue = $objWidget->value;