[Non-BE] Resolve "MC encoder crashing with bitrate and bandwidth switching"

• Related issues: #986 (closed)
• Requested reviewers: @bayers @fotopoulou

Reason why this change is needed

• Fixes crashes in MC with bitrate and bandwidth switching

Description of the change

• Changes the usage and setting of bandwidth parameter in MCT and MDCT-CPE
• IGF flag is initialized using a different bandwidth variable
• A USAN error in the MCT encoder was fixed as well - it did only show up now with the newly added testcases

Affected operating points

• MC bitrate and bandwidth switching

Related to #986 (closed)