Add NULL check in fillGlyphBufferForRun
Add NULL check in fillGlyphBufferForRun

Add check to fillGlyphBufferForRun and fillGlyphBufferForTextEmphasisRun
for a NULL run and if so exit early. Individual runs can be NULL if they
consist entierly of control characters and thus have a glyph count of 0.

BUG=508613
R=leviw@chromium.org

Review URL: https://codereview.chromium.org/1226143008

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@198636 bbb929c8-8fbe-4397-9dbb-9b2b20218538

Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk