Ignore SDO transfers not initiated by our device

Author: wilkinsw

package.json

@@ -1,6 +1,6 @@
 {
   "name": "canopen",
-  "version": "2.8.0",
+  "version": "2.8.1",
   "description": "CANopen implementation for Javascript",
   "main": "index.js",
   "scripts": {

source/protocol/sdo.js

@@ -953,7 +953,7 @@ class Sdo {
     _onMessage(message) {
         // Handle transfers as a client (remote object dictionary)
         const serverTransfer = this.transfers[message.id];
-        if(serverTransfer) {
+        if(serverTransfer !== undefined && serverTransfer.active) {
             switch(message.data[0] >> 5) {
                 case ServerCommand.ABORT:
                     serverTransfer.abort(message.data.readUInt32LE(4));