Eliminate division warning of blackbody_wn_rad2temp

[chorng]

Code Sample, a minimal, complete, and verifiable piece of code

with np.errstate(divide='ignore', invalid='ignore'):
    return PLANCK_C1 * wavenumber / np.log((PLANCK_C2 * wavenumber**3) / radiance + 1.0)

Problem description

The blackbody_wn_rad2temp function is currently raising runtime warning when encountering divide by zero, which is not the same behavior as other functions, e.g. the planck function.

Expected Output

No warning is raised when encountering divide by zero.

Actual Result, Traceback if applicable

RuntimeWarning: divide by zero encountered in divide
return PLANCK_C1 * wavenumber / np.log((PLANCK_C2 * wavenumber**3) / radiance + 1.0)

Versions of Python, package at hand and relevant dependencies

Python 3.10, pyspectral 0.13.5

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