[3GPP-Issue #824] Fixes crash in low level signal at 24.4 kbps with dtx enabled

[x] The crash (mentioned in issue #824 ) was occurring in function stereo_dft_generate_comfort_noise_fx(). The shr() in the IF condition overflow. Using shr_sat solved the issue.

Pipeline results:

• EVS 26.444 BE test passes.
• decoder pytests:
  MLD scores:
  Original inputs: 562 failed, 374 skipped
  MLD > 10: 28
  MLD > 5 : 85
  MLD < 5 : 449
  +10dB inputs: 562 failed, 374 skipped
  MLD > 10: 128
  MLD > 5 : 183
  MLD < 5 : 251
  -10dB inputs: 562 failed, 374 skipped
  MLD > 10: 5
  MLD > 5 : 38
  MLD < 5 : 519
• encoder pytests results:
  MLD scores:
  Original inputs: 562 tests:
  MLD > 10: 18
  MLD > 5 : 71
  MLD < 5 : 473
  +10dB inputs: 562 tests:
  MLD > 10: 66
  MLD > 5 : 124
  MLD < 5 : 372
  -10dB inputs: 562 tests:
  MLD > 10: 5
  MLD > 5 : 30
  MLD < 5 : 527