Use `async` a bit more in the API
Use `async` a bit more in the API

This patch changes the `PDFDocumentLoadingTask.destroy`-method and the `_fetchDocument`-function to be `async`, which slightly simplifies the relevant code.

Furthermore, remove the catch-handler from the `WorkerTransport.getPageIndex`-method since it's no longer needed. Given that the `MessageHandler` is nowadays wrapping every possible Exception, it's no longer necessary to try and re-wrap the reason here.

xavier114fch/pdf.js,Snuffleupagus/pdf.js,mozilla/pdf.js,mozilla/pdf.js,showpad/mozilla-pdf.js,Shoobx/pdf.js,nawawi/pdf.js,Snuffleupagus/pdf.js,nawawi/pdf.js,showpad/mozilla-pdf.js,macroplant/pdf.js,nawawi/pdf.js,showpad/mozilla-pdf.js,timvandermeij/pdf.js,Shoobx/pdf.js,timvandermeij/pdf.js,macroplant/pdf.js,xavier114fch/pdf.js,Shoobx/pdf.js,macroplant/pdf.js,timvandermeij/pdf.js,mozilla/pdf.js,Snuffleupagus/pdf.js