Let `goldstein` filtering work with partial blocks, mask the result after to match the original

[scottstanie]

By ignoring anything with a nan in it, the goldstein filtered ifg loses a bunch of pixels in blocks around the edge

There's multiple ways we could fix it; one is to run nan_to_num and keep everything else the same, resulting in something like this

which we could then mask based on the original nodata region:

[scottstanie]

closed by #447