optimize: Add a unit test when the initial F is NaN or Inf about gonum

[btracey]

We have this now in getStartingLocation. Were you looking for something else?

[vladimir-ch]

Er, I meant "unit test" or whatever these go test things are called. Just for completeness and safety.

[vladimir-ch]

Again, I don't recall what exactly I intended with this, it was in my beginnings with Go/Gonum. But now that we have this here anyway: we check for NaN or Inf in the local methods in getStartingLocation but perhaps we could check the initial location at a higher level in Minimize.

[vladimir-ch]

I checked the code again and I think it is best to leave it up to individual methods how they deal with NaN/Inf initial function values.