[RFA] libiberty/hashtab.c, higher_prime_index: avoid array overrun

[DJ Delorie]

Bizzare, the problem isn't the hash loop, it's the error handler at
the end!  It never uses [30] for the main loop, only if you give it a
number between 0xfffffffb and 0xffffffff - and in the case where it
would use [30], it's supposed to abort anyway.

I couldn't figure out why your patch worked until I realized that the
main loop still fails!  It works because the error handler just
doesn't abort, returning the last array entry, which happens to be the
right one.

I think a suitable comment explaining what's actually going on, and
why it still works, is warranted... but your patch is OK with me
otherwise :-)