API returns 405 for malformed address

### Subject of the issue
The native Algorand API returns a 405 error for a malformed address sent to the GET /v1/address/ endpoint.

### Your environment
{"versions":["v1"],"genesis_id":"mainnet-v1.0","genesis_hash_b64":"wGHE2Pwdvd7S12BL5FaOP20EGYesN73ktiC1qzkkit8=","build":{"major":2,"minor":0,"build_number":4,"commit_hash":"729b125a","branch":"rel/stable","channel":"stable"}}

### Steps to reproduce
curl -v -H "X-Algo-API-Token: $(cat ./data/algod.token)" http://127.0.0.1:48081/v1/account/dfsfsdsadf

### Expected behaviour
Should either get a 400 for a bad request or a 500 for internal server error, or the specification should be updated to include a 405 error, even a generic catch-all

### Actual behaviour
< HTTP/1.1 405 Method Not Allowed
< Date: Mon, 09 Mar 2020 14:47:56 GMT
< Content-Length: 0