Don't try to delete file if it doesn't exist

youtube_dlc/postprocessor/embedthumbnail.py

@@ -91,6 +91,7 @@ class EmbedThumbnailPP(FFmpegPostProcessor):
         elif info['ext'] == 'mkv':
             old_thumbnail_filename = thumbnail_filename
             thumbnail_filename = os.path.join(os.path.dirname(old_thumbnail_filename), 'cover.jpg')
+            if os.path.exists(thumbnail_filename):
                 os.remove(encodeFilename(thumbnail_filename))
             os.rename(encodeFilename(old_thumbnail_filename), encodeFilename(thumbnail_filename))