Prevent crash

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

@@ -88,18 +88,21 @@ public class WorkerCleanup extends Worker {
                 List<Long> mids = db.message().getMessageWithContent();
                 for (Long mid : mids) {
                     EntityMessage message = db.message().getMessage(mid);
+                    if (message != null) {
                         File file = message.getFile(context);
                         if (!file.exists()) {
                             Log.w("Message file missing id=" + mid);
                             db.message().setMessageContent(mid, false);
                         }
                     }
+                }
 
                 // Check attachments files
                 Log.i("Checking attachments files");
                 List<Long> aids = db.attachment().getAttachmentAvailable();
                 for (Long aid : aids) {
                     EntityAttachment attachment = db.attachment().getAttachment(aid);
+                    if (attachment != null) {
                         File file = attachment.getFile(context);
                         if (!file.exists()) {
                             Log.w("Attachment file missing id=" + aid);
@@ -107,6 +110,7 @@ public class WorkerCleanup extends Worker {
                         }
                     }
                 }
+            }
 
             long now = new Date().getTime();