Check user interrupt in geos_distance_indexed

[paleolimbot]

No description provided.

[paleolimbot]

(Reminding myself that this is hard to do because you can't longjmp from the callback)

[paleolimbot]

Punting for now, but one could check this by unwind-protecting or try/catch on R_CheckUserInterrupt()...the trick would be figuring out how to do it intermittently (maybe through a global variable). You can return 0 from the callback to stop processing and throw an error.

[paleolimbot]

This can be done much more easily in C++ using cpp11 infrastructure...for now it would need a C-level unwind protect I think.