$interpolate 'allOrNothing' ignores empty case

[amitport]

Do you want to request a feature or report a bug?
bug

What is the current behavior?
$interpolate service when running with allOrNothing, does not pass the value if there's nothing to interpolate (this affects ngAtrr*, which does not write the corresponding attribute when it has a simple value)

If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem via https://plnkr.co or similar (template: http://plnkr.co/edit/tpl:yBpEi4).
http://plnkr.co/edit/1QhnA9xb5BgyzWHpeL7O?p=preview

What is the expected behavior?
should see the poster image on video...

What is the motivation / use case for changing the behavior?
Although there is no real need for using ngAttr/ngSrc/ngHref without interpolation, it's sometimes useful to do so when exploring initial html template or learning angular. Having to use ng-attr-*="{{'value'}}" instead of ng-attr-*="value" is not intuitive.

Which versions of Angular, and which browser / OS are affected by this issue? Did this work in previous versions of Angular? Please also test with the latest stable and snapshot (https://code.angularjs.org/snapshot/) versions.
angular 1.5.8
win 7
chrome 53, IE 11, firefox 47

Other information (e.g. stacktraces, related issues, suggestions how to fix)
following #15130 (comment)

[Narretz]

I think this is a valid problem, and it would be good to align this with normal attribute handling (which allows static values for obvious reasons).

[gkalpak]

I don't think this has anything to do with allOrNothing. It is because when there is no interpolation symbol, then $interpolate returns undefined, which cause the internal interpolate directive to bail out early (without setting the attribute value). It makes sense in most cases, because the attribute is already set, but in the case of ngAttr we need to explicitly set the corresponding attribute.

[gkalpak]

I submitted a possible fix in #15149.