Add class_exists check for FFmpeg VideoInfo class

Fix: Fatal error when FFmpeg addon is installed but class not loaded
- Check if FFmpeg addon is available (isAvailable)
- Check if VideoInfo class exists (class_exists)
- Prevents fatal error if addon is in wrong state
- Gracefully returns null if FFmpeg not ready

Error was: Class FriendsOfRedaxo\FFmpeg\VideoInfo not found

Author: skerbis

lib/BackendIntegration.php

@@ -65,12 +65,16 @@ private static function renderFFmpegInfo(string $filename): ?string
             return null;
         }
 
+        // Check if FFmpeg VideoInfo class exists
+        if (!class_exists('\FriendsOfRedaxo\FFmpeg\VideoInfo')) {
+            return null;
+        }
+
         if (PlatformDetector::isAudio($filename)) {
             return null;
         }
 
         try {
-            /** @phpstan-ignore undefinedClass */
             $videoInfo = \FriendsOfRedaxo\FFmpeg\VideoInfo::getBasicInfo($filename);
 
             if (!$videoInfo) {