undefined behavior in bitstream.c

Upstream appears to be effectively dead, but there's undefined behavior happening here:

```
Illegal instruction at address 0x4ace666
/home/andy/.cache/zig/p/1220a15af8fd1628f0adfeb43782c49cdbe0ea8d45922f8f23772a2a4d0e2df7e072/libmp3lame/bitstream.c:181:50: 0x4ace666 in putbits2 (/home/andy/.cache/zig/p/1220a15af8fd1628f0adfeb43782c49cdbe0ea8d45922f8f23772a2a4d0e2df7e072/libmp3lame/bitstream.c)
bs->buf[bs->buf_byte_idx] |= ((val >> j) << bs->buf_bit_idx);
^
/home/andy/.cache/zig/p/1220a15af8fd1628f0adfeb43782c49cdbe0ea8d45922f8f23772a2a4d0e2df7e072/libmp3lame/bitstream.c:627:9: 0x4ad1f9a in Huffmancode (/home/andy/.cache/zig/p/1220a15af8fd1628f0adfeb43782c49cdbe0ea8d45922f8f23772a2a4d0e2df7e072/libmp3lame/bitstream.c)
putbits2(gfc, (int)ext, xbits);
^
/home/andy/.cache/zig/p/1220a15af8fd1628f0adfeb43782c49cdbe0ea8d45922f8f23772a2a4d0e2df7e072/libmp3lame/bitstream.c:649:12: 0x4acf8ef in ShortHuffmancodebits (/home/andy/.cache/zig/p/1220a15af8fd1628f0adfeb43782c49cdbe0ea8d45922f8f23772a2a4d0e2df7e072/libmp3lame/bitstream.c)
bits = Huffmancode(gfc, gi->table_select[0], 0, region1Start, gi);
^
/home/andy/.cache/zig/p/1220a15af8fd1628f0adfeb43782c49cdbe0ea8d45922f8f23772a2a4d0e2df7e072/libmp3lame/bitstream.c:718:34: 0x4aca7d5 in writeMainData (/home/andy/.cache/zig/p/1220a15af8fd1628f0adfeb43782c49cdbe0ea8d45922f8f23772a2a4d0e2df7e072/libmp3lame/bitstream.c)
data_bits += ShortHuffmancodebits(gfc, gi);
^
/home/andy/.cache/zig/p/1220a15af8fd1628f0adfeb43782c49cdbe0ea8d45922f8f23772a2a4d0e2df7e072/libmp3lame/bitstream.c:932:13: 0x4ac41b1 in format_bitstream (/home/andy/.cache/zig/p/1220a15af8fd1628f0adfeb43782c49cdbe0ea8d45922f8f23772a2a4d0e2df7e072/libmp3lame/bitstream.c)
bits += writeMainData(gfc);
^
/home/andy/.cache/zig/p/1220a15af8fd1628f0adfeb43782c49cdbe0ea8d45922f8f23772a2a4d0e2df7e072/libmp3lame/encoder.c:544:12: 0x4b86665 in lame_encode_mp3_frame (/home/andy/.cache/zig/p/1220a15af8fd1628f0adfeb43782c49cdbe0ea8d45922f8f23772a2a4d0e2df7e072/libmp3lame/encoder.c)
(void) format_bitstream(gfc);
^
/home/andy/.cache/zig/p/1220a15af8fd1628f0adfeb43782c49cdbe0ea8d45922f8f23772a2a4d0e2df7e072/libmp3lame/lame.c:1793:19: 0x4a4daa3 in lame_encode_buffer_sample_t (/home/andy/.cache/zig/p/1220a15af8fd1628f0adfeb43782c49cdbe0ea8d45922f8f23772a2a4d0e2df7e072/libmp3lame/lame.c)
ret = lame_encode_mp3_frame(gfc, mfbuf[0], mfbuf[1], mp3buf, buf_size);
^
/home/andy/.cache/zig/p/1220a15af8fd1628f0adfeb43782c49cdbe0ea8d45922f8f23772a2a4d0e2df7e072/libmp3lame/lame.c:1904:20: 0x4a43b23 in lame_encode_buffer_template (/home/andy/.cache/zig/p/1220a15af8fd1628f0adfeb43782c49cdbe0ea8d45922f8f23772a2a4d0e2df7e072/libmp3lame/lame.c)
return lame_encode_buffer_sample_t(gfc, nsamples, mp3buf, mp3buf_size);
^
/home/andy/.cache/zig/p/1220a15af8fd1628f0adfeb43782c49cdbe0ea8d45922f8f23772a2a4d0e2df7e072/libmp3lame/lame.c:1915:12: 0x4a43903 in lame_encode_buffer (/home/andy/.cache/zig/p/1220a15af8fd1628f0adfeb43782c49cdbe0ea8d45922f8f23772a2a4d0e2df7e072/libmp3lame/lame.c)
return lame_encode_buffer_template(gfp, pcm_l, pcm_r, nsamples, mp3buf, mp3buf_size, pcm_short_type, 1, 1.0);
^
/home/andy/.cache/zig/p/1220e5bb0972b1f7e009566ddcf705d0b5ba049a4616f0a65fd97295e64fe0b3022a/libavcodec/libmp3lame.c:210:13: 0x4a2719d in mp3lame_encode_frame (/home/andy/.cache/zig/p/1220e5bb0972b1f7e009566ddcf705d0b5ba049a4616f0a65fd97295e64fe0b3022a/libavcodec/libmp3lame.c)
ENCODE_BUFFER(lame_encode_buffer, int16_t, frame->data);
^
/home/andy/.cache/zig/p/1220e5bb0972b1f7e009566ddcf705d0b5ba049a4616f0a65fd97295e64fe0b3022a/libavcodec/encode.c:264:11: 0x39fcfda in ff_encode_encode_cb (/home/andy/.cache/zig/p/1220e5bb0972b1f7e009566ddcf705d0b5ba049a4616f0a65fd97295e64fe0b3022a/libavcodec/encode.c)
ret = codec->cb.encode(avctx, avpkt, frame, got_packet);
^
/home/andy/.cache/zig/p/1220e5bb0972b1f7e009566ddcf705d0b5ba049a4616f0a65fd97295e64fe0b3022a/libavcodec/encode.c:350:15: 0x3a07fbc in encode_simple_internal (/home/andy/.cache/zig/p/1220e5bb0972b1f7e009566ddcf705d0b5ba049a4616f0a65fd97295e64fe0b3022a/libavcodec/encode.c)
ret = ff_encode_encode_cb(avctx, avpkt, frame, &got_packet);
^
/home/andy/.cache/zig/p/1220e5bb0972b1f7e009566ddcf705d0b5ba049a4616f0a65fd97295e64fe0b3022a/libavcodec/encode.c:364:15: 0x3a0774b in encode_simple_receive_packet (/home/andy/.cache/zig/p/1220e5bb0972b1f7e009566ddcf705d0b5ba049a4616f0a65fd97295e64fe0b3022a/libavcodec/encode.c)
ret = encode_simple_internal(avctx, avpkt);
^
/home/andy/.cache/zig/p/1220e5bb0972b1f7e009566ddcf705d0b5ba049a4616f0a65fd97295e64fe0b3022a/libavcodec/encode.c:398:15: 0x3a00166 in encode_receive_packet_internal (/home/andy/.cache/zig/p/1220e5bb0972b1f7e009566ddcf705d0b5ba049a4616f0a65fd97295e64fe0b3022a/libavcodec/encode.c)
ret = encode_simple_receive_packet(avctx, avpkt);
^
/home/andy/.cache/zig/p/1220e5bb0972b1f7e009566ddcf705d0b5ba049a4616f0a65fd97295e64fe0b3022a/libavcodec/encode.c:541:15: 0x39fe627 in avcodec_send_frame (/home/andy/.cache/zig/p/1220e5bb0972b1f7e009566ddcf705d0b5ba049a4616f0a65fd97295e64fe0b3022a/libavcodec/encode.c)
ret = encode_receive_packet_internal(avctx, avci->buffer_pkt);
^
```