ocioconvert silently errors out when given invalid bitdepth running on Windows

[KevinJW]

When calling ocioconvert from a terminal on windows and an invalid bitdepth is given, it does not output the intended error message:

https://github.com/AcademySoftwareFoundation/OpenColorIO/blob/main/src/apps/ocioconvert/main.cpp#L142

This is because the throw is not within a try/catch block and exceptions produce no output unless you do something with them.

Suggest turning this into a simple std:cerr message and exit() with an appropriate error code.

[Ayush-Mittal10]

I want to work on it. How can I start?