Decoder crash for MC51 at 512kbps FER in LFE PLC

Closely related to #922 (closed). The fixed point decoder crashes in basop32.c with an assert, this time in a different function.

Frames processed:       767     Assertion failed: (0), function saturate, file basop32.c, line 507.

Steps to reproduce:

./IVAS_cod_flt_ref -mc 5_1 -max_band FB 512000 48 experiments/basop-verification/MC-5_1/proc_input/am2aa1s05.wav out/mc-5_1--am2aa1s05--512000.192
eid-xor -vbr -fer out/mc-5_1--am2aa1s05--512000.192 error_patterns/mc-5_1--am2aa1s05--512000_ep.192 out/mc-5_1--am2aa1s05--512000.fer.192
./IVAS_dec_fx 5_1 48 out/mc-5_1--am2aa1s05--512000.fer.192 out/mc-5_1--am2aa1s05--512000.fer.dec.fx.wav

Float reference SHA (_flt_ref): d9fdb374

FX binary SHA (_fx): 2470528b

Error pattern file: mc-5_1--am2aa1s05--512000_ep.192

Bitstream can be shared upon request.