pinky,who: fix bug in latest change

* src/system.h (stzncpy): New function.
* src/pinky.c (print_entry): Use stzncpy, not stpncpy.
The latter does not NUL-terminate.  I assumed that strncpy was
the only function with such a horrible API.  Today I learned that
stpncpy also may not NUL-terminate its result.
The bugs were introduced in commit v8.17-48-gf79263d.
* src/who.c (print_user): Likewise.
Thanks to Erik Auerswald for spotting my error.

1 files changed, 14 insertions, 0 deletions

diff --git a/src/system.h b/src/system.h
index 5e3b3cbde..6907603e6 100644
--- a/src/system.h
+++ b/src/system.h
@@ -626,6 +626,20 @@ The following directory is part of the cycle:\n  %s\n"), \
     }					\
   while (0)
 
+/* Like stpncpy, but do ensure that the result is NUL-terminated,
+   and do not NUL-pad out to LEN.  I.e., when strnlen (src, len) == len,
+   this function writes a NUL byte into dest[len].  Thus, the destination
+   buffer must be at least LEN+1 bytes long.  */
+static inline char *
+stzncpy (char *dest, char const *src, size_t len)
+{
+  char const *src_end = src + len;
+  while (src < src_end && *src)
+    *dest++ = *src++;
+  *dest = 0;
+  return dest;
+}
+
 #ifndef ARRAY_CARDINALITY
 # define ARRAY_CARDINALITY(Array) (sizeof (Array) / sizeof *(Array))
 #endif