Try to create Typeface before writing to config file

This is additional guard for preventing unusable font files for update.

Bug: 187542525
Test: atest FontFamilyUpdateRequestTest
Test: atest FontListParserTest
Test: atest FontManagerTest
Test: atest NativeSystemFontTest
Test: atest PersistentSystemFontConfigTest
Test: atest SystemFontsTest
Test: atest SystemFontsUniqueNameTest
Test: atest UpdatableFontDirTest
Test: atest UpdatableSystemFontTest
Change-Id: I61060e19e0e8c9b1ee992ab85eb93562ea823e5e