respond with 422 or 400 code on invalid address

--- ~ » curl -k -i --silent --max-time 10 -X GET -d address="fingerprint=1D55273DF749B45A52B946C98FB14A7CE04F4F18" https://unstable.bitmask.net:6425
HTTP/1.1 500 Internal Server Error
Date: Tue, 06 Dec 2016 15:03:34 GMT
Server: Apache
Content-Length: 24
X-Frame-Options: DENY
Connection: close

500 Not a valid address



--- ~ » gpg --search-keys 1D55273DF749B45A52B946C98FB14A7CE04F4F18
gpg: data source: https://sks.spodhuis.org:443
(1)	rsa2048 (Example RSA 2048bit key) 
	  2048 bit RSA key 0x8FB14A7CE04F4F18, created: 2016-12-05
Keys 1-1 of 1 for "1D55273DF749B45A52B946C98FB14A7CE04F4F18".  Enter number(s), N)ext, or Q)uit > 

(from redmine: created on 2016-12-06, closed on 2016-12-06, relates #8648 (closed))