bug: error on load of exchange pacakge

[RyanConway91]

Describe the bug
I am trying to load a model where a local disv (quadtree (layer, node)) is nested in a regional dis (regular (layer, row, column)) model. The model runs fine in MF6 with no errors. However, when I try and load in flopy I get:

Here is the top of .exg package

Desktop (please complete the following information):

• OS: Windows
• Version: flopy = '3.3.7'

[spaulins-usgs]

@RyanConway91, just merged a fix for this. Please check out the latest develop branch and confirm that this fixes your problem.

[wpbonelli]

removing from 3.4.3 milestone as the fix for this touches files to be introduced in 3.5.0