fix handling of nil session in reattach code

irc/accounts.go

@@ -238,7 +238,10 @@ func (am *AccountManager) BouncerAllowed(account string, session *Session) bool
 	if !config.Accounts.Bouncer.Enabled {
 		return false
 	}
-	return config.Accounts.Bouncer.AllowedByDefault || session.capabilities.Has(caps.Bouncer)
+	if config.Accounts.Bouncer.AllowedByDefault {
+		return true
+	}
+	return session != nil && session.capabilities.Has(caps.Bouncer)
 }
 
 // Looks up the enforcement method stored in the database for an account

irc/client_lookup_set.go

@@ -152,7 +152,7 @@ func (clients *ClientManager) SetNick(client *Client, session *Session, newNick
 
 	currentClient := clients.byNick[newcfnick]
 	// the client may just be changing case
-	if currentClient != nil && currentClient != client {
+	if currentClient != nil && currentClient != client && session != nil {
 		// these conditions forbid reattaching to an existing session:
 		if client.Registered() || !bouncerAllowed || account == "" || account != currentClient.Account() || client.isTor != currentClient.isTor || client.HasMode(modes.TLS) != currentClient.HasMode(modes.TLS) {
 			return errNicknameInUse