DevTools: Do not show go to line dialog when there is no open tab in the editor.

BUG=358102
R=apavlov@chromium.org, apavlov, pfeldman

Review URL: https://codereview.chromium.org/238243004

git-svn-id: svn://svn.chromium.org/blink/trunk@171549 bbb929c8-8fbe-4397-9dbb-9b2b20218538