Ugly RuntimeWarning in bose_factor

[rebeccafair]

Sometimes on this line in StructureFactor._bose_factor:

Euphonic/euphonic/structure_factor.py

Line 338 in ef49d8b

bose = 1/(np.exp(np.absolute(self._frequencies)/(kB*temp)) - 1)

RuntimeWarning: overflow encountered in exp is triggered.

This happens if the temperature is low and mode frequencies are high, I encountered this with an Ammonium Sulphate calculation that I have (mode frequencies up to 425 meV) and a temperature of 5K, but you can reproduce this with any material if you set the temperature to a silly small value.

I don't think we need to change the result (we get an infinite exponential and then bose = 0 which is what we want), but when using euphonic-powder-map it screws with the progress bar so we may want to hide this warning sometimes.