fix znc.in/playback for individual DM targets

This is a regression introduced in 0d05ab4ff4; playback for an individual
DM target would play all DMs.

irc/client.go

 	}
 	if !session.autoreplayMissedSince.IsZero() && !hasHistoryCaps {
 		rb := NewResponseBuffer(session)
-		zncPlayPrivmsgs(client, rb, "", time.Now().UTC(), session.autoreplayMissedSince)
+		zncPlayPrivmsgsFromAll(client, rb, time.Now().UTC(), session.autoreplayMissedSince)
 		rb.Send(true)
 	}
 	session.autoreplayMissedSince = time.Time{}

irc/znc.go

 	}
 
 	if playPrivmsgs {
-		zncPlayPrivmsgs(client, rb, "", start, end)
+		zncPlayPrivmsgsFromAll(client, rb, start, end)
 	}
 
 	rb.session.zncPlaybackTimes = &zncPlaybackTimes{
 	}
 
 	for _, cfNick := range nickTargets {
-		zncPlayPrivmsgs(client, rb, cfNick, start, end)
+		zncPlayPrivmsgsFrom(client, rb, cfNick, start, end)
 		rb.Flush(true)
 	}
 }
 
-func zncPlayPrivmsgs(client *Client, rb *ResponseBuffer, target string, start, end time.Time) {
-	_, sequence, _ := client.server.GetHistorySequence(nil, client, target)
-	if sequence == nil {
+func zncPlayPrivmsgsFrom(client *Client, rb *ResponseBuffer, target string, start, end time.Time) {
+	_, sequence, err := client.server.GetHistorySequence(nil, client, target)
+	if sequence == nil || err != nil {
 		return
 	}
+	zncMax := client.server.Config().History.ZNCMax
+	items, err := sequence.Between(history.Selector{Time: start}, history.Selector{Time: end}, zncMax)
+	if err == nil && len(items) != 0 {
+		client.replayPrivmsgHistory(rb, items, target)
+	}
+}
+
+func zncPlayPrivmsgsFromAll(client *Client, rb *ResponseBuffer, start, end time.Time) {
 	zncMax := client.server.Config().History.ZNCMax
 	items, err := client.privmsgsBetween(start, end, maxDMTargetsForAutoplay, zncMax)
 	if err == nil && len(items) != 0 {