[Skia] Crash when failing to create a font with custom data

https://bugs.webkit.org/show_bug.cgi?id=271391

Reviewed by Adrian Perez de Castro.

This happens for example with test
fast/css/font-face-data-uri-invalid.html. SkFontMgr::makeFromData()
fails to create the SkTypeface and returns nullptr that we don't check.

* Source/WebCore/platform/graphics/skia/FontCustomPlatformDataSkia.cpp:
(WebCore::FontCustomPlatformData::create):

Canonical link: https://commits.webkit.org/276473@main

Source/WebCore/platform/graphics/skia/FontCustomPlatformDataSkia.cpp

@@ -102,6 +102,9 @@ FontPlatformData FontCustomPlatformData::fontPlatformData(const FontDescription&
 RefPtr<FontCustomPlatformData> FontCustomPlatformData::create(SharedBuffer& buffer, const String& itemInCollection)
 {
     sk_sp<SkTypeface> typeface = FontCache::forCurrentThread().fontManager()->makeFromData(buffer.createSkData());
+    if (!typeface)
+        return nullptr;
+
     FontPlatformData::CreationData creationData = { buffer, itemInCollection };
     return adoptRef(new FontCustomPlatformData(WTFMove(typeface), WTFMove(creationData)));
 }