fix arguments check in sslhandshake

Author: chronolaw

lib/resty/core/socket.lua

@@ -177,7 +177,7 @@ local function sslhandshake(cosocket, reused_session, server_name, ssl_verify,
     local n = select("#", ...)
     if not cosocket or n > 1 then
         error("ngx.socket sslhandshake: expecting 1 ~ 5 arguments " ..
-              "(including the object), but seen " .. (5 + n))
+              "(including the object), but seen " .. (cosocket and 5 + n or 0))
     end
 
     local r = get_request()