fix auth errors when username/password are too long (#1482)

Author: Jakub Adamus

Diff for: AUTHORS

@@ -51,6 +51,7 @@ ICHINOSE Shogo <shogo82148 at gmail.com>
 Ilia Cimpoes <ichimpoesh at gmail.com>
 INADA Naoki <songofacandy at gmail.com>
 Jacek Szwec <szwec.jacek at gmail.com>
+Jakub Adamus <kratky at zobak.cz>
 James Harr <james.harr at gmail.com>
 Janek Vedock <janekvedock at comcast.net>
 Jason Ng <oblitorum at gmail.com>

Diff for: packets.go

@@ -394,7 +394,7 @@ func (mc *mysqlConn) writeHandshakeResponsePacket(authResp []byte, plugin string
 // http://dev.mysql.com/doc/internals/en/connection-phase-packets.html#packet-Protocol::AuthSwitchResponse
 func (mc *mysqlConn) writeAuthSwitchPacket(authData []byte) error {
 	pktLen := 4 + len(authData)
-	data, err := mc.buf.takeSmallBuffer(pktLen)
+	data, err := mc.buf.takeBuffer(pktLen)
 	if err != nil {
 		// cannot take the buffer. Something must be wrong with the connection
 		mc.log(err)