Prevent crash

app/src/main/java/eu/faircode/email/MessageHelper.java

@@ -769,6 +769,7 @@ public class MessageHelper {
                     });
                     attachmentPart.setDataHandler(new DataHandler(dataSource));
 
+                    if (attachment.name != null)
                         attachmentPart.setFileName(attachment.name);
                     if (attachment.disposition != null)
                         attachmentPart.setDisposition(attachment.disposition);