Simplify the code

Author: gkubisa

lib/client/doc.js

@@ -106,9 +106,13 @@ Doc.prototype.destroy = function(callback) {
   doc.whenNothingPending(function() {
     if (doc.wantSubscribe) {
       doc.unsubscribe(function(err) {
-        if (!err) doc.connection._destroyDoc(doc);
-        if (callback) return callback(err);
-        if (err) this.emit('error', err); 
+        if (err) {
+          if (callback) callback(err);
+          else this.emit('error', err);
+          return;
+        }
+        doc.connection._destroyDoc(doc);
+        if (callback) callback();
       });
     } else {
       doc.connection._destroyDoc(doc);