Correctly handle errors from getSession

cmd/frontend/pdf.go

@@ -15,6 +15,8 @@ import (
 func UploadPDF(c *b.Config, s *b.CookieStore) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		if _, err := getSession(w, r, c, s); err != nil {
+			log.Println(err)
+			http.Error(w, err.Error(), http.StatusInternalServerError)
 			return
 		}