[third_party] Restrict libpng visibility to existing users

Fix typo

Bug: 77808
Change-Id: Ic6314bf1f37ad98169c54a7d218f570273c7d9e1
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/libpng/+/537121
Reviewed-by: Shai Barack <shayba@google.com>
1 file changed