tok3_encode_names crashes on arm on invalid input

[shubhamchandak94]

Hi, I observed that tok3_encode_names crashes on ARM but not x86_64 when providing an input
blk = [128, 10] (byte 128 followed by newline), level = 7, use_arith=false. Instead of 128, higher bytes also cause this issue.

Commit used: 2aca18b

lscpu:

Architecture:           aarch64
  CPU op-mode(s):       32-bit, 64-bit
  Byte Order:           Little Endian
CPU(s):                 8
  On-line CPU(s) list:  0-7
Vendor ID:              ARM
  Model name:           Neoverse-N1
    Model:              1
    Thread(s) per core: 1
    Core(s) per socket: 8
    Socket(s):          1
    Stepping:           r3p1
    BogoMIPS:           243.75
    Flags:              fp asimd evtstrm aes pmull sha1 sha2 crc32 atomics fphp asimdhp cpuid asimdrdm lrcpc dcpop asimddp ssbs

Trace:

==70891== Process terminating with default action of signal 6 (SIGABRT): dumping core
==70891==    at 0x4A68454: __pthread_kill_implementation (in /usr/lib64/libc.so.6)
==70891==    by 0x4A1F31F: raise (in /usr/lib64/libc.so.6)
==70891==    by 0x4A06223: abort (in /usr/lib64/libc.so.6)
==70891==    by 0x14C9EB: build_trie (tokenise_name3.c:496)
==70891==    by 0x14C9EB: tok3_encode_names (tokenise_name3.c:1459)
==70891==    by 0x14C9EB: tok3_encode_names (tokenise_name3.c:1431)

[jkbonfield]

I may be a signed vs unsigned char issue and a last of an explicit cast somewhere, but I though the latest change disallowed anything more than 7-bit ASCII.

I'll have an explore. Thanks.