Renderer config reader: fix for erroneous acoustic environment structure access

• Related issues: #1020 (closed)
• Requested reviewers: @kiene

Reason why this change is needed

While running decoder application with a custom renderer configuration including multiple acoustic environments, errors were observed while selecting one of the configurations.

Description of the change

Fixed erroneous access to the acoustic environment ID.

Affected operating points

Rendering using renderer configuration file containing multiple acoustic environments.

Related to #1020 (closed)