index: fix lazy indexing

After the previous changes

lib/index/mu-indexer.cc

@@ -158,17 +158,14 @@ Indexer::Private::handler(const std::string& fullpath, struct stat* statbuf,
 		// is up-to-date (this is _not_ always true; hence we call it
 		// lazy-mode); only for actual message dirs, since the dir
 		// tstamps may not bubble up.
-		if (conf_.lazy_check)  {
-			dirstamp_ = store_.dirstamp(fullpath);
-			if (dirstamp_ >= statbuf->st_ctime &&
+		dirstamp_ = store_.dirstamp(fullpath);
+		if (conf_.lazy_check && dirstamp_ >= statbuf->st_ctime &&
 			    htype == Scanner::HandleType::EnterNewCur) {
 				mu_debug("skip {} (seems up-to-date: {:%FT%T} >= {:%FT%T})",
 					 fullpath, mu_time(dirstamp_), mu_time(statbuf->st_ctime));
 				return false;
 			}
-		} else
-			dirstamp_ = 0;
-
+		}
 		// don't index dirs with '.noindex'
 		auto noindex = ::access((fullpath + "/.noindex").c_str(), F_OK) == 0;
 		if (noindex) {