Prevent crash

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

@@ -3506,7 +3506,7 @@ public class AdapterMessage extends RecyclerView.Adapter<AdapterMessage.ViewHold
             boolean current = properties.getValue(full ? "full" : "images", message.id);
             boolean asked = properties.getValue(full ? "full_asked" : "images_asked", message.id);
             if (current || asked) {
-                if (current) {
+                if (current && message.from != null) {
                     SharedPreferences.Editor editor = prefs.edit();
                     for (Address sender : message.from) {
                         String from = ((InternetAddress) sender).getAddress();