Add more validation in PDFWorker.fromPort

The signature of the `PDFWorker.fromPort` method, in addition to the `PDFWorker` constructor, was changed in PR 9480.
Hence it's probably a good idea to add a bit more validation to `PDFWorker.fromPort`, to ensure that it won't fail silently for an API consumer that updates to version 2.0 of the PDF.js library.

src/display/api.js

@@ -1593,6 +1593,9 @@ var PDFWorker = (function PDFWorkerClosure() {
    * @param {PDFWorkerParameters} params - The worker initialization parameters.
    */
   PDFWorker.fromPort = function(params) {
+    if (!params || !params.port) {
+      throw new Error('PDFWorker.fromPort - invalid method signature.');
+    }
     if (pdfWorkerPorts.has(params.port)) {
       return pdfWorkerPorts.get(params.port);
     }