RenormalizedAngularMomentum fails with FindRoot method and small frequency

[barrywardell]

The FindRoot method in RenormalizedAngularMomentum currently fails when given a very low frequency. For example the following returns $Failed:

RenormalizedAngularMomentum[-2, 2, 0, 0, 0.00001, 4, Method -> "FindRoot"]

as does the same thing with a good initial guess:

RenormalizedAngularMomentum[-2, 2, 0, 0, 0.00001, 4, Method -> {"FindRoot", "InitialGuess" -> 2}]

[barrywardell]

The test case has changed since commit 95a805b. A new example is
RenormalizedAngularMomentum[-2, 2, 0, 0, 0.000005, 4, Method -> {"FindRoot", "InitialGuess" -> 2}]

[barrywardell]

A simple fix is to use higher precision, i.e.

RenormalizedAngularMomentum[-2, 2, 0, 0, 0.000005`32, 4, 
 Method -> {"FindRoot", "InitialGuess" -> 2.000000001`32}]

We could consider using the series expansion in this case.