Return error 400 instead of 500 on invalid path part
Current behaviour:
`curl corp.short.cm/%AF` returns `500 Internal Server Error`
Expected:
`curl corp.short.cm/%AF` returns `400 Invalid request`

I'm running a link shortener service and user put different combinations in path part, some of them are valid, some of them - not. This case I sent is a client error and there is no need to raise an exception here