[FastTextAutosizer] Fix crash on empty tables

Empty tables would assert because they do not create clusters but we
(correctly) assert in inflateTable() that the current cluster is a
table. This patch only calls inflateTable() if a cluster was created.

BUG=347395
NOTRY=true

Review URL: https://codereview.chromium.org/181433014

git-svn-id: svn://svn.chromium.org/blink/trunk@168058 bbb929c8-8fbe-4397-9dbb-9b2b20218538