IDL: Use implicit false in compute_info_individual()

This is a minor style correction. We'd prefer the 'implicit false' rather
than 'len(array) > 0'.

Review URL: https://codereview.chromium.org/678453004

git-svn-id: svn://svn.chromium.org/blink/trunk@184324 bbb929c8-8fbe-4397-9dbb-9b2b20218538