reset mShapingPaint's SkTypeface before we use it

Harfbuzz works in TTF glyph-space, but most of Skia works in
fallback glyph-space. shapeFontRun() helpfully calculates the
baseGlyphCount needed to convert between the two, but leaves
mShapingPaint's SkTypeface set to the specific TTF being shaped
rather than the original SkTypeface that was requested. Needless
to say, this causes all manner of horrific malady when glyph
indices are calculated in one glyph-index-space and then applied
to another.

To fix this issue, I reset mShapingPaint's SkTypeface when done
with the Harfbuzz shaping operation so that the baseGlyphCount only
gets applied once.

Change-Id: Ia886f89d667634e15e5fc8d7af443c9d1ba89622