[Non BE] Add fix for non-diegetic panning flag encoding when extended metadata is not enabled

• Related issues: #746 (closed)
• Requested reviewers: @kiene

Reason why this change is needed

The metadata encoder encodes the azimuth as a panning gain even though extended metadata is not enabled. This crashes the decoder since it puts the encoder and decoder out-of-synch.

Description of the change

Adds a condition to also check the ism_extended_metadata_flag before writing the non-diegetic panning flag.

#ifdef NONBE_FIX_746_NONDIEGETIC_MD
                if ( hIsmMeta[ch]->non_diegetic_flag && ism_extended_metadata_flag )
#else
                if ( hIsmMeta[ch]->non_diegetic_flag )
#endif

Affected operating points

Affects ISM cases where the non-diegetic panning flag is set and the extended metadata is not enabled (using the + sign or bit rate below 64 kbps).