Handle NULL FontData in Font::glyphDataAndPageForCharacter
Handle NULL FontData in Font::glyphDataAndPageForCharacter

The FontFallbackList::fontDataAt method may return null when a font data
object is requested yet in Font::glyphDataAndPageForCharacter we wrongly
assume it always returns a non-null value. This cause a null dereference
crash in the rather rare cases where a null FontData object is returned.

Fix by changing glyphDataAndPageForCharacter to fall back on the primary
font, which is guaranteed to exist, if the fallback list returned a null
FontData object.

BUG=446566
R=szager@chromium.org

Review URL: https://codereview.chromium.org/839623003

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@187939 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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