Nested compound datatypes report error values on Windows

[mattjala]

Additional testing is needed to replicate this and determine if the type of data in the lowest layer (vlen strings vs. other) plays a role. I was unable to replicate this on Ubuntu using the attached file, but I did discover some related issues fixed in #467

The attached script will create an HDF5 file with several types of dataset with various levels of nesting, and should be used to try and replicate this.

Error was reported with HDFView 3.4.1

create_string_dset.py

[mattjala]

On a Windows 10 VM, I didn't find any issue opening any of the datasets in the testing file. The root problem may involve a different kind of dataset, or rely on a different environment.