Handle cancel for default download path in Linux sandbox

Telegram/SourceFiles/core/file_utilities.cpp

@@ -195,6 +195,7 @@ QString DefaultDownloadPath(not_null<Main::Session*> session) {
 			Core::App().saveSettings();
 			return result;
 		}
+		return QString();
 	}
 	return realDefaultPath;
 }

Telegram/SourceFiles/data/data_document.cpp

@@ -155,6 +155,7 @@ QString FileNameUnsafe(
 			return path;
 		}
 	}();
+	if (path.isEmpty()) return QString();
 	if (name.isEmpty()) name = qsl(".unknown");
 	if (name.at(0) == QChar::fromLatin1('.')) {
 		if (!QDir().exists(path)) QDir().mkpath(path);

Telegram/SourceFiles/media/view/media_view_overlay_widget.cpp

@@ -1750,6 +1750,7 @@ void OverlayWidget::downloadMedia() {
 	} else {
 		path = Core::App().settings().downloadPath();
 	}
+	if (path.isEmpty()) return;
 	QString toName;
 	if (_document) {
 		const auto &location = _document->location(true);