[Tizen][Runtime] Fix can not open blocked http/https pages in external web browser.

There's a bug in the logic of open external url, all http/https pages will not
be opend in external web browser. This patch will fix it.

BUG=XWALK-1605
Merge pull request #2595 from takethathe/external_uri

[Tizen][Runtime] Fix can not open blocked http/https pages in external web browser