Diff between doc and code for GEOSisValidReason_r

[BuonOmo]

In the documentation, it is said that an empty string will be return for a valid geometry, however, we get "Valid Geometry".

It seems pretty easy to fix, let me know to which version you want to stick (I prefer the empty string) and I'll do it :)

[pramsey]

I think the doc needs the change, we can't flip the behaviour.