Fixed some unused-but-set-variable warnings.

Telegram/SourceFiles/storage/file_download_web.cpp

@@ -418,7 +418,7 @@ void WebLoadManager::failed(
 }
 
 void WebLoadManager::failed(int id, not_null<QNetworkReply*> reply) {
-	if (const auto sent = findSent(id, reply)) {
+	if ([[maybe_unused]] const auto sent = findSent(id, reply)) {
 		removeSent(id);
 		queueFailedUpdate(id);
 	}

Telegram/SourceFiles/storage/storage_media_prepare.cpp

@@ -319,7 +319,7 @@ void PrepareDetails(PreparedFile &file, int previewWidth, int sideLimit) {
 			file.preview.setDevicePixelRatio(style::DevicePixelRatio());
 			file.type = PreparedFile::Type::Video;
 		}
-	} else if (const auto song = std::get_if<Song>(&file.information->media)) {
+	} else if (v::is<Song>(file.information->media)) {
 		file.type = PreparedFile::Type::Music;
 	}
 }