Try to fix orphanedAttachments.

Thanks to Madko and xet7 !

Related #2776

server/publications/attachments.js

@@ -34,27 +34,32 @@ Meteor.publish('attachmentsList', function() {
 
 Meteor.publish('orphanedAttachments', function() {
   let keys = [];
-  Attachments.find({}, { fields: { copies: 1 } }).forEach(att => {
-    keys.push(new ObjectID(att.copies.attachments.key));
-  });
-  keys.sort();
-  keys = _.uniq(keys, true);
 
-  return AttachmentStorage.find(
-    { _id: { $nin: keys } },
-    {
-      fields: {
-        _id: 1,
-        filename: 1,
-        md5: 1,
-        length: 1,
-        contentType: 1,
-        metadata: 1,
-      },
-      sort: {
-        filename: 1,
+  if (Attachments.find({}, { fields: { copies: 1 } }) !== undefined) {
+    Attachments.find({}, { fields: { copies: 1 } }).forEach(att => {
+      keys.push(new ObjectID(att.copies.attachments.key));
+    });
+    keys.sort();
+    keys = _.uniq(keys, true);
+
+    return AttachmentStorage.find(
+      { _id: { $nin: keys } },
+      {
+        fields: {
+          _id: 1,
+          filename: 1,
+          md5: 1,
+          length: 1,
+          contentType: 1,
+          metadata: 1,
+        },
+        sort: {
+          filename: 1,
+        },
+        limit: 250,
       },
-      limit: 250,
-    },
-  );
+    );
+  } else {
+    return [];
+  }
 });