Avoid reading pass the end of the source buffer when it is not NUL

terminated.

If this buffer is adjacent to an unmapped page or a version of C with
bounds checked is used this may result in a crash.

PR:		206178
Submitted by:	Alexander Cherepanov <cherepan@mccme.ru>
MFC after:	1 week

lib/libc/string/wcslcat.c

@@ -54,7 +54,7 @@ wcslcat(wchar_t *dst, const wchar_t *src, size_t siz)
 	size_t dlen;
 
 	/* Find the end of dst and adjust bytes left but don't go past end */
-	while (*d != '\0' && n-- != 0)
+	while (n-- != 0 && *d != '\0')
 		d++;
 	dlen = d - dst;
 	n = siz - dlen;