Fix layer box error on window minimize

Thank you to @audioglider for catching and reporting
Start of pdPackage interface

Layer support obviously requires that PD read/write a custom PhotoDemon
file format that preserves full image data, including all layer data.
This is a daunting task, and one that could be a big headache if not
done right.

To that end, I've been working on a zip-like file format for creating
PDI ("PhotoDemon Image") files.  The neat thing about this zip-like
format is that it's completely data-agnostic, meaning it could be used
by any VB project to read and write zip-like archive files of any type
of data.

I call these files "pdPackage" files.  The file format supports a bunch
of neat features, including compression (via zLib), CRC32 validation,
fixed-width directory structs (for great performance), loading
individual nodes without decompressing the entire archive, and more.
Just like PD's XML engine, this will have many uses beyond just PDI
files; in fact, once it's done, I'm going to move all PNG icon assets
into a standalone pdPackage file, which will allow for multiple icon
sets, as has been discussed with @Kroc.

Anyway, the archive file interface is still obviously a long ways from
being functional, but as I wanted to sync a bug-fix from @audioglider,
this is going up too.  Layer work is temporarily suspended until I get
this working, because it's tedious to constantly create layered image
files for testing.  I'd much rather create several and save them to
file...  (Also, I need this before I can get Undo/Redo working again.)