Improve error message in matching

[lcarver]

If you are trying to match in transfer line mode and you add a linopt constraint for the tune, it is very possible that your machine is not stable. In this case, the optics constraints evaluate nicely, but then for the tune you get a NaN and you get the following error

ValueError: Residuals are not finite in the initial point.

This could probably be caught and a more helpful error message given.