PromotedLinkTraffic: better handle campaigns that end early.

r2/r2/lib/pages/trafficpages.py

@@ -638,6 +638,12 @@ class PromotedLinkTraffic(Templated):
         """Shorten range for display and add next/prev buttons."""
         start, end = promote.get_traffic_dates(thing)
 
+        # Check date of latest traffic (campaigns can end early).
+        history = get_promo_traffic(thing, start, end)
+        end = max(date for date, data in history)
+        end = end.replace(tzinfo=g.tz)  # get_promo_traffic returns tz naive
+                                        # datetimes but is actually g.tz
+
         if self.period:
             display_start = self.after
             display_end = self.before