fixed invalid links on images when DriveCache was disabled

cache-images.go

@@ -511,6 +511,8 @@ func serveMissingImage(w http.ResponseWriter, r *http.Request) {
 	w.Header().Set("Cache-Control", "no-store, must-revalidate")
 	w.Header().Set("Pragma", "no-cache")
 	w.Header().Set("Expires", "0")
-	w.WriteHeader(http.StatusNotFound)
+	if config.DriveCacheEnabled {
+		w.WriteHeader(http.StatusNotFound)
+	}
 	http.ServeFile(w, r, missingImagePath)
 }