[BUGFIX] Determine preview mode for v9

As the Context is introduced in v10 to TypoScriptFrontendController and
therefore PreviewAspect cannot be determined, in v9 the preview mode is
checked in a different way. This bugfix respects the non-existing
Context and PreviewAspect in TYPO v9 to determine the correct behaviour
in the renderDeeplPreviewFlag

Author: calien666

Classes/Hooks/DeeplPreviewFlagGeneratePageHook.php

@@ -4,6 +4,8 @@
 
 namespace WebVision\WvDeepltranslate\Hooks;
 
+use TYPO3\CMS\Core\Information\Typo3Version;
+use TYPO3\CMS\Core\Utility\GeneralUtility;
 use TYPO3\CMS\Frontend\Controller\TypoScriptFrontendController;
 
 class DeeplPreviewFlagGeneratePageHook
@@ -15,8 +17,13 @@ public function renderDeeplPreviewFlag(array $params): void
     {
         $controller = $params['pObj'];
 
-        $isInPreviewMode = $controller->getContext()->hasAspect('frontend.preview')
-            && $controller->getContext()->getPropertyFromAspect('frontend.preview', 'isPreview');
+        $typo3Version = GeneralUtility::makeInstance(Typo3Version::class);
+        if ($typo3Version->getMajorVersion() < 10) {
+            $isInPreviewMode = (bool)$controller->fePreview;
+        } else {
+            $isInPreviewMode = $controller->getContext()->hasAspect('frontend.preview')
+                && $controller->getContext()->getPropertyFromAspect('frontend.preview', 'isPreview');
+        }
         if (
             !$isInPreviewMode
             || $controller->doWorkspacePreview()