ArgumentOutOfRangeException with certain input

[TechGoon]

Hello!

I've been messing around with different inputs to understand WFC better, and hit a case that throws an exception, and I'm not sure whether this is a bug or just a combination of inputs that it can't handle.

To reproduce the issue, use this input image:

and add this line to samples.xml
<overlapping name="mine02" N="3" periodicInput="False" periodic="False" />

The result is:

< mine02
> CONTRADICTION
> DONE
Unhandled exception. System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection. (Parameter 'index')
   at System.Collections.Generic.List`1.get_Item(Int32 index)
   at OverlappingModel.Save(String filename) in D:\dev\WaveFunctionCollapse\OverlappingModel.cs:line 116
   at Program.Main() in D:\dev\WaveFunctionCollapse\Program.cs:line 59

Looking at the code, I can see that the value at the requested index of the observed array is still -1 from being Clear()ed, so the patterns array is, understandably, upset about that.

Thank you for your time!