Fixed tests
Fixed tests

* Fixed usage of `np.ma.MaskedArray`. Masked arrays are not very useful in numpy, so 0 is used to indicate a non-edge index.
* Fixed fragile testing of edge finding above/below the threshold. With a high threshold, it's possible to find an edge in the middle of the test subject's face, which then causes tests to fail. Fixed by filtering parts of the edge with a 0 index.

TadLeonard/crash-kiss,TadLeonard/crash-kiss,TadLeonard/crash-kiss