Fix buffer overflow with invalid quotes (#209)

A follow-up commit to 6f49ad0.
The quotes can have their upper bits set in which case more than just
two digits are printed, eventually overflowing the allocated memory.

How to reproduce:

less --quotes=$(echo -e '\xff\xff') -f /dev/null
Then enter "-T x" to trigger lglob function

filename.c

@@ -757,7 +757,8 @@ lglob(filename)
  */
  len = (int) (strlen(lessecho) + strlen(filename) + (7*strlen(metachars())) + 24);
  cmd = (char *) ecalloc(len, sizeof(char));
- SNPRINTF4(cmd, len, "%s -p0x%x -d0x%x -e%s ", lessecho, openquote, closequote, esc);
+ SNPRINTF4(cmd, len, "%s -p0x%x -d0x%x -e%s ", lessecho,
+ (unsigned char) openquote, (unsigned char) closequote, esc);
  free(esc);
  for (s = metachars(); *s != '\0'; s++)
  sprintf(cmd + strlen(cmd), "-n0x%x ", (unsigned char) *s);