Prevent NPE

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

@@ -614,6 +614,7 @@ public class EntityMessage implements Serializable {
             template_reply = template_reply.replace("$to$", MessageHelper.formatAddresses(to));
             template_reply = template_reply.replace("$cc$", MessageHelper.formatAddresses(cc));
             template_reply = template_reply.replace("$time$", date);
+            if (subject != null)
                 template_reply = template_reply.replace("$subject$", subject);
             p.html(template_reply);
         }