only apply fuzzy topic logic to actually orphaned emails

if there is no IRT or References set, it's fair to assume this is meant
as a new topic.
diff --git a/site/api/stats.lua b/site/api/stats.lua
index a564622..6ca6f97 100644
--- a/site/api/stats.lua
+++ b/site/api/stats.lua
@@ -636,7 +636,7 @@
                     irt = irt:gsub("^[a-zA-Z]+:%s+", "")
                 end
             end
-            local point = emails[irt] or findSubject(emails, emls, irt, email.epoch)
+            local point = emails[irt] or ((email['in-reply-to'] or email['references']) and findSubject(emails, emls, irt, email.epoch))
             if point then
                 if point.nest < 50 then
                     point.nest = point.nest + 1