External renderer CLI problems

Basic info

• Commit SHA: 605ee559
• Platform: MacOS

Bug description

I've encountered some problems with the command line interface of the external renderer:

1. IVAS_rend crashes with ISM input when the -im flag missing.
2. Confusing error message with invalid option -ism (missing number of objects)

Ways to reproduce

1. IVAS_rend -i scripts/testv/test_ISM_1obj.wav -if ism1 -o out.wav -of STEREO
2. IVAS_rend -i scripts/testv/test_ISM_1obj.wav -if ism -im scripts/testv/stvISM1.csv -o out.wav -of STEREO gives error message: Missing required argument: input_format (if)