Fix Java API error where requesting another style for a provided family fails

Internally the API uses the same code path as SkTypeface::CreateFromName which
returns NULL if the requested style is not supported by the existing family.
However, the existing Java API expects that we return the default font in the
requested style so this CL ensures that we do.

bug: 10860066
Change-Id: Ide3a0cc24015e97fa35aef283b42e7d7d11edd9c