Un-ratelimit calls to /thumbnail (#2251)

mediaapi/routing/routing.go

@@ -120,6 +120,8 @@ func makeDownloadAPI(
 		w.Header().Set("Content-Type", "application/json")
 
 		// Ratelimit requests
+		// NOTSPEC: The spec says everything at /media/ should be rate limited, but this causes issues with thumbnails (#2243)
+		if name != "thumbnail" {
 			if r := rateLimits.Limit(req); r != nil {
 				if err := json.NewEncoder(w).Encode(r); err != nil {
 					w.WriteHeader(http.StatusInternalServerError)
@@ -128,6 +130,7 @@ func makeDownloadAPI(
 				w.WriteHeader(http.StatusTooManyRequests)
 				return
 			}
+		}
 
 		vars, _ := httputil.URLDecodeMapValues(mux.Vars(req))
 		serverName := gomatrixserverlib.ServerName(vars["serverName"])