Skip FontFamily creation if the font files don't exists.

Bug: 186580197
Test: atest FontFamilyUpdateRequestTest FontListParserTest
      FontManagerTest NativeSystemFontTest
      PersistentSystemFontConfigTest SystemFontsTest
      SystemFontsUniqueNameTest UpdatableFontDirTest
      UpdatableSystemFontTest
Change-Id: Ibbcfb9ed43d05dd9db0132f3a7cb0321243be054
4 files changed