user agent if Endpoint is not started yet

lib/pleroma/application.ex

@@ -22,6 +22,7 @@ def named_version, do: @name <> " " <> @version
   def repository, do: @repository
 
   def user_agent do
+    if Process.whereis(Pleroma.Web.Endpoint) do
       case Config.get([:http, :user_agent], :default) do
         :default ->
           info = "#{Pleroma.Web.base_url()} <#{Config.get([:instance, :email], "")}>"
@@ -30,6 +31,10 @@ def user_agent do
         custom ->
           custom
       end
+    else
+      # fallback, if endpoint is not started yet
+      "Pleroma Data Loader"
+    end
   end
 
   # See http://elixir-lang.org/docs/stable/elixir/Application.html