Fix uninitialized variables in HarfBuzzShaperBase
https://bugs.webkit.org/show_bug.cgi?id=79546

Reviewed by Dirk Pranke.

These were introduced in r108733.

* platform/graphics/harfbuzz/HarfBuzzShaperBase.cpp:
(WebCore::HarfBuzzShaperBase::HarfBuzzShaperBase):

git-svn-id: svn://svn.chromium.org/blink/trunk@108871 bbb929c8-8fbe-4397-9dbb-9b2b20218538