[FIX] #47057 UI: ensure one selected Field\Select option. (ILIAS-eLearning#11009)

* Fixes https://mantis.ilias.de/view.php?id=47057
* Update empty value check

Author: fhelfer

components/ILIAS/UI/src/Implementation/Component/Input/Field/Renderer.php

@@ -488,25 +488,26 @@ public function renderSelectField(F\Select $component, RendererInterface $defaul
         $this->applyName($component, $tpl);
 
         $value = $component->getValue();
+        $value_is_empty = $value === null || $value === '';
         //disable first option if required.
         $tpl->setCurrentBlock("options");
-        if (!$value) {
+        if ($value_is_empty) {
             $tpl->setVariable("SELECTED", 'selected="selected"');
         }
-        if ($component->isRequired() && !$value) {
+        if ($value_is_empty && $component->isRequired()) {
             $tpl->setVariable("DISABLED_OPTION", "disabled");
             $tpl->setVariable("HIDDEN", "hidden");
         }
 
-        if (!($value && $component->isRequired())) {
+        if ($value_is_empty || !$component->isRequired()) {
             $tpl->setVariable("VALUE", null);
             $tpl->setVariable("VALUE_STR", $component->isRequired() ? $this->txt('ui_select_dropdown_label') : '-');
             $tpl->parseCurrentBlock();
         }
 
         foreach ($component->getOptions() as $option_key => $option_value) {
             $tpl->setCurrentBlock("options");
-            if ($value == $option_key) {
+            if (!$value_is_empty && $value == $option_key) {
                 $tpl->setVariable("SELECTED", 'selected="selected"');
             }
             $tpl->setVariable("VALUE", $option_key);