BUNIT map header appears to be case sensitive

[ajm-ska]

Describe the bug
We have received a helpdesk ticket from a user who has an issue with a header in their image files. BUNIT = 'Jy/Beam' results in the statistics widget showing NaN for FluxDensity. The user discovered that if they modify the header to BUNIT = 'Jy/beam', then CARTA correctly displays the FluxDensity value. The user says the same problem occurs in both CARTA v2.0 and v3.0.

To Reproduce
I have not personally tried it, but perhaps modify the BUNIT header in a FITS file from 'Jy/Beam' to 'Jy/beam' and check the FluxDensity value in the statistics widget each time.

Expected behavior
I assume it should not be case sensitive and any combination of Jy/Beam, Jy/Beam or JY/BEAM should work?