Avoid calling ExecuteCode() on a NULL TabContents. The problem was an extra...

Avoid calling ExecuteCode() on a NULL TabContents. The problem was an extra set of parens were missing, so the "not" operator only applied to the GetTabById() return value.

BUG=34778

Review URL: http://codereview.chromium.org/1238001

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@42421 0039d316-1c4b-4281-b951-d872f2087c98