`await controller.openDocument()` is not being waited on

[dcupidon]

Describe the bug Other DocumentViewController methods are running before openDocument() finishes even though the await keyword is being used. When debugging with Android Studio, I realized that onTabDocumentLoaded was not being called after openDocument.

Steps to Reproduce the Problem

1. Use example/lib/main.dart and uncomment the code needed to use the widget view.
2. In onDocumentViewCreated place any method call after await controller.openDocument(_document, config: config);, where _document = "https://pdftron.s3.amazonaws.com/downloads/pl/PDFTRON_mobile_about.pdf"
3. Run app

Expected behavior The document would have opened as normal and the methods called would have ran in order.

Screenshots Call stack:

Platform/Device Information (please complete the following information if applicable):

• Platform: Android
• Device: Pixel 3a
• OS: Android 11