Resolve "IVAS_rend ignores missing ISM metadata files"

• Related issues: #1373 (closed)
• Requested reviewers: @malenovsky

Reason why this change is needed

• Silently ignoring missing metadata is dangerous in batch processing scenarios

Description of the change

• Error is thrown if there exists an ISM input without a corresponding metadata file path

Affected operating points

• CLI of IVAS_rend for input configurations containing ISM inputs

Related to #1373 (closed)