Prevent undefined error on null object when calling .destroy on a

document initialized with LocalPdfManager.

Per @brendandahl's recommendation, moved the terminate function out of worker
and into the PdfManager

src/core/worker.js

@@ -368,7 +368,7 @@ var WorkerMessageHandler = PDFJS.WorkerMessageHandler = {
     });
 
     handler.on('Terminate', function wphTerminate(data, promise) {
-      pdfManager.streamManager.networkManager.abortAllRequests();
+      pdfManager.terminate();
       promise.resolve();
     });
   }