x can become NaN

[James Cook]

I've found that x can become NaN during a run, but the solve is not terminated. This line

NLsolve.jl/src/nlsolve/utils.jl

Line 19 in 9b4c7b3

 if !any(isnan, x_previous) && chebyshev(x, x_previous) <= xtol 

appears to be related and seems to indicate that NaNs are acceptable, and presumably may turn back to regular numbers. Is this right?

[Patrick Kofod Mogensen]

I would not expect them to. That should stop if it sees NaN. I'm not sure why it's written like that. Thanks.

[James Cook]

No probs 😄

[Patrick Kofod Mogensen]

#244 should fix this