Actually WAIT for the PDF to load

[sithel]

Thanks to Kameron for raising this issue by finding it with a 784 page PDF....

In async openpdf(file) { we have this.currentdoc = await PDFDocument.load(this.input); and I can see us hit that, pause, and then wait for... yikes, it took ~60 seconds on my machine? With no UI updates (looks broken) and then we eventually progress beyond that step.

Need to add some sort of UI to reflect this progress

[sithel]

Rhi saw some weird switching-between-PDFs behavior, I think might also be caused by this?

When addressed, reference this msg to see if resolved: https://discord.com/channels/726108551428440206/953709370267541634/1068385723583041637