Resolve "[MSAN Clang 18] use-of-uninitialized value in open_decoder_LPD"

• Related issues: #1385 (closed)
• Requested reviewers: @fotopoulou

Reason why this change is needed

Make sure hIGFDec->infoIGFStopFreq is initialized.

Description of the change

• Describe what is done.

Affected operating points

• All should stay BE.

Related to #1385 (closed)