Fix uninitialized face in fx_ge_font.cpp

MSAN reported this issue when I tried to reproduce 460936 in the last version of freetype on Linux.

BUG=N/A
R=thestig@chromium.org

Review URL: https://codereview.chromium.org/1050333002

(cherry picked from commit 672bd1706a990069dce401afead6c2ecfcdb3357)

Review URL: https://codereview.chromium.org/1136943003