fix crash cowboy when socket close


[error] Ranch listener boss_http_listener had connection 
here the log:
process started with cowboy_protocol:start_link/4 at <0.283.0> exit with reason: {{case_clause,closed},[{cowboy_protocol,execute,4,[{file,"src/cowboy_protocol.erl"},{line,529}]}]}
Merge pull request #1 from mihawk/patch-1

fix crash cowboy when socket close