Fix bug 8717690 Full-width Latin Letters Garbled on Tumblr App

For fullwidth latin (or, more generally, a font considered as a complex
script, but not supported by the font specified), and for a font other
than a system default font, we were getting a mismatch in baseGlyphCount
between the shaping and painting fonts.

This patch preserves the original typeface in this case. In that sense,
it is a slightly more general fix for bug 8127795.

Change-Id: Ibdbfdb34eb7dc39cc8f0784a67c93c9af4ce6ab2