Give a clear error if using a path that falls outside of the cube footprint

[astrofrog]

I can post a specific example later, but I noticed that if using e.g. PathFromCenter with a path that falls way outside the image, one can get an exception if the WCS starts returning NaN values.

[keflavich]

WCS returning NaN isn't a 'fall outside of footprint' error, is it? Isn't that more of a ... wrapped around the sky sort of issue, or something along those lines?

[astrofrog]

Yeah, in my case the coordinates were really really wrong and it was on the other side of the sky.