Non-exisiting page accesses are not handled correctly

[nak3]

Please check following reproduce steps:

step1. Start dingo

$ go run main.go
Database is used at dingo.db
Application Started on port 8000

step2. Access to invalid page (before login)

e.g. http://localhost:8000/foo

This steps produces 500 Internal error with go panic.

[dinever]

Thanks. I'm going to fix this and add some test cases.