Make errors fatal for typefaces w/o PNG decoding registered

Fontations and DirectWrite will silently (in release) fail if
they cannot decode a PNG file. If a PNG decoder is not registered,
we want that to be a loud failure.

Change-Id: Ie694ed14af8ff6e1e1e3984a90fe9de1d2bbdf6e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1113977
Commit-Queue: Kaylee Lubick <kjlubick@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>