Only print entries for which ut_host points to a character device.

Now that we use utmpx, we more often have entries for which the ut_line
is left blank. To prevent us from returning struct stat for "/dev/",
check that the resulting stat structure belongs to a character device.

usr.bin/w/w.c

@@ -497,7 +497,7 @@ ttystat(char *line)
 	char ttybuf[MAXPATHLEN];
 
 	(void)snprintf(ttybuf, sizeof(ttybuf), "%s%s", _PATH_DEV, line);
-	if (stat(ttybuf, &sb) == 0) {
+	if (stat(ttybuf, &sb) == 0 && S_ISCHR(sb.st_mode)) {
 		return (&sb);
 	} else
 		return (NULL);