libiberty: potential bugs in mkstemps

I have noticed that the implementation of `mkstemps` in libiberty will 
silently accept a negative `suffix_len`.  A negative `suffix_len` is 
always incorrect, and in this case it may allow for out-of-bounds access:

   int
   mkstemps (char *pattern, int suffix_len)
   {
[...]
     size_t len;
     int count;

     len = strlen (pattern);

     if ((int) len < 6 + suffix_len
         || strncmp (&pattern[len - 6 - suffix_len], "XXXXXX", 6))
       {
         return -1;
       }

     XXXXXX = &pattern[len - 6 - suffix_len];

Is the omission of this check intentional?  If so, what's the reason? 
glibc's implementation checks it.

Something else that seems to be missing: according to the man page, when 
the above check fails, errno should be set to `EINVAL`.  Again, that's 
what glibc does.  Is not setting it intentional as well?

If any or both of the above cases are bugs, I will submit a patch.

Tomás