Emission costs output doesn't work

[tsmbland]

I get this error when I use the emission_costs output:

  File "C:\Users\tbland\Documents\Code\MUSE_OS\src\muse\outputs\mca.py", line 871, in sector_emission_costs
    i = (np.where(envs))[0][0]
        ~~~~~~~~~~~~~~~~~~~^^^
IndexError: index 0 is out of bounds for axis 0 with size 0

This happens both with MUSE 1.1.0 and the dev version

Relates to the sector_emission_costs function in outputs/mca.py