Use nullptr to indicate C locale when using xlocale

BUG=chromium:666228

Change-Id: I951102eba2b79ddaa5eb134834471a4a3ec8aed7
Reviewed-on: https://skia-review.googlesource.com/6603
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
1 file changed