[Android] Expand the path of app_root in LaunchScreen

If the provided path of manifest.json is not absolute, the launch screen image can not be found
and will cause build fail.
Change to use ManifestParser.input_path.

BUG=XWALK-1795
[Android] Add validation for get navigation item

If the input parameter is out of scope, it will cause crash.
Add validation here to avoid crash.

BUG=XWALK-1863
Merge pull request #2044 from kurli/validate_history_index

[Android] Add validation for get navigation item
Merge pull request #2014 from kurli/launchscreen_expand_apth

[Android] Expand the path of app_root in LaunchScreen