interfering talker flag not triggered on short test vector

Basic info

• Encoder (float): 311956f3
• Encoder (fix) : e1432023
• Decoder: 311956f3

Bug description

The interfering talker flag is not triggered on stvST48c.wav, leading to a lower quality for stereo content during interfering content.

in the figure below, from top to bottom :

• synthesis (stvST48c.wav)
• floating point element mode
• fixed point element mode

Ways to reproduce

IVAS_cod -STEREO 24400 48 .\ivas-codec\scripts\testv\stvST48c.wav bit24400

(Clear steps or refer to a failing automated test, e.g. with a pipeline link)

tagging @malenovsky, @multrus for awareness