Skip nil messages in send loops

Added checks to skip nil messages in message sending loops for `client_119.go` and `client_120.go`. This prevents potential nil pointer dereference and ensures the send logic handles only valid messages.

Author: wneessen

client_119.go

@@ -44,6 +44,9 @@ func (c *Client) SendWithSMTPClient(client *smtp.Client, messages ...*Msg) error
 	}
 	var errs []*SendError
 	for id, message := range messages {
+		if message == nil {
+			continue
+		}
 		if sendErr := c.sendSingleMsg(client, message); sendErr != nil {
 			messages[id].sendError = sendErr
 

client_120.go

@@ -50,6 +50,9 @@ func (c *Client) SendWithSMTPClient(client *smtp.Client, messages ...*Msg) (retu
 	}()
 
 	for id, message := range messages {
+		if message == nil {
+			continue
+		}
 		if sendErr := c.sendSingleMsg(client, message); sendErr != nil {
 			messages[id].sendError = sendErr
 			errs = append(errs, sendErr)