Only include the avatar attachment if is going to show a message in the invitation (#12747)

app/email.go

@@ -445,11 +445,13 @@ func (a *App) SendGuestInviteEmails(team *model.Team, channels []*model.Channel,
 			}
 
 			embeddedFiles := make(map[string]io.Reader)
+			if message != "" {
 				if senderProfileImage != nil {
 					embeddedFiles = map[string]io.Reader{
 						"user-avatar.png": bytes.NewReader(senderProfileImage),
 					}
 				}
+			}
 
 			if err := a.SendMailWithEmbeddedFiles(invite, subject, bodyPage.Render(), embeddedFiles); err != nil {
 				mlog.Error(fmt.Sprintf("Failed to send invite email successfully err=%v", err))