CB-6940: context.getExternal* methods return null if sdcard isn't in mounted state, causing exceptions that prevent startup from reaching readystate

Signed-off-by: Joe Bowser <bowserj@apache.org>
CB-6940: Android: cleanup try/catch exception handling

Signed-off-by: Joe Bowser <bowserj@apache.org>
CB-6940: Fixing up commit from dzeims