Fix #3871 (#4082)

src/misc/get-drive-file-url.ts

@@ -4,15 +4,17 @@ import config from '../config';
 export default function(file: IDriveFile, thumbnail = false): string {
 	if (file == null) return null;
 
+	const isImage = file.contentType && file.contentType.startsWith('image/');
+
 	if (file.metadata.withoutChunks) {
 		if (thumbnail) {
-			return file.metadata.thumbnailUrl || file.metadata.webpublicUrl || file.metadata.url;
+			return file.metadata.thumbnailUrl || file.metadata.webpublicUrl || (isImage ? file.metadata.url : null);
 		} else {
 			return file.metadata.webpublicUrl || file.metadata.url;
 		}
 	} else {
 		if (thumbnail) {
-			return `${config.drive_url}/${file._id}?thumbnail`;
+			return isImage ? `${config.drive_url}/${file._id}?thumbnail` : null;
 		} else {
 			return `${config.drive_url}/${file._id}?web`;
 		}