EVS: bug in ACELP music post-processor

In the EVS part, ACELP decoder, there is a bug in the signal extrapolation of the LD music post-processor. The function Prep_music_postP_fx() should be called with the argument st->last_core and not st->last_coder_type.

A fix is as follows (function acelp_core_dec_fx()):

#ifdef FIX
    Prep_music_postP_fx( exc_buffer_fx, dct_buffer_fx, st->hMusicPF->filt_lfE_fx, st->last_core, st->element_mode, pitch_buf_fx, st->hMusicPF->LDm_enh_lp_gbin_fx, st->Q_exc, &qdct )
#else
    Prep_music_postP_fx( exc_buffer_fx, dct_buffer_fx, st->hMusicPF->filt_lfE_fx, st->last_coder_type, st->element_mode, pitch_buf_fx, st->hMusicPF->LDm_enh_lp_gbin_fx, st->Q_exc, &qdct )
 #endif

The IVAS part is correct.