DevTools: [Console] fix sourceurl when exception happens before inspector is open

When exception happens before inspector is open source url (from //# sourceURL=) is correctly shown in console.

Review URL: https://codereview.chromium.org/260513004

git-svn-id: svn://svn.chromium.org/blink/trunk@176862 bbb929c8-8fbe-4397-9dbb-9b2b20218538