Also try initializing _distro_series earlier

src/source_package_publishing_history.cpp

@@ -27,6 +27,7 @@ source_package_publishing_history::source_package_publishing_history()
       self_link(""),
       distro_series_link(""),
       lp(nullptr),
+      _distro_series(nullptr),
       distro_series([this]() -> std::optional<::distro_series> {
           if (distro_series_link.empty()) return std::nullopt;
           if (_distro_series) return _distro_series;