crypt: remove dubious validator.

The validate_salt function was introduced in commit
c3a0ceb2cea1a9d43f2baf5a2e63d0d712c8df19, February 2020.
I cannot reproduce the internal crash in crypt which
it alleges, and I neglected to mention the bad inputs
in the commit or add tests. I'm not able to reproduce
the alleged behavior in spite of trying all sorts of bad
inputs; and looking at the crypt source in glibc, I
don't see any obvious problem.

And so, on this Halowe'en, we exorcise the ghost
that has been haunting the crypt.

* sysif.c (salt_char_p, validate_salt): Static functions
removed.
(crypt_wrap): Don't call validate_salt, and so cwsalt
need not be tested for null.

* tests/018/crypt.tl: New file.

* txr.1: Mention that crypt_r is used if available, which
avoids static storage.

1 files changed, 7 insertions, 2 deletions

diff --git a/txr.1 b/txr.1
index 959dbe33..d6278481 100644
--- a/txr.1
+++ b/txr.1
@@ -72856,8 +72856,13 @@ platform function. The hash value is assumed to be UTF-8 and converted to
 Unicode characters, though it is not expected to contain anything but 7
 bit ASCII characters.
 
-Note: the underlying C library function uses a static buffer for its return
-value. The return value of the \*(TL function is a copy of that buffer.
+Note: if C library function
+.code crypt
+uses a static buffer for its return value. If that function is used,
+the Lisp string returned by the \*(TL function carries its own copy of
+that buffer. Where available, the
+.code crypt_r
+function is used which avoids static storage.
 
 .SS* Unix Signal Handling