Hide the tooltip when its content becomes empty

[merrihew]

When the tooltip's content becomes empty (set to null), if the tooltip is currently open I think it should be closed. This is related to closed issue #129 , but it's different than the original issue and wasn't addressed in 030901e.

Here is my suggested modification to tooltip.js

attrs.$observe( type, function ( val ) {
    if ( !val && scope.tt_isOpen ) {
        hide();
        if ( angular.isDefined( scope.tt_animation ) && scope.tt_animation() ) {
            transitionTimeout = $timeout( function () { scope.tt_content = val; }, 500 );
        } else {
            scope.tt_content = val;
        }
    } else {
        scope.tt_content = val;
    }
});

Without the if/else statement the tooltip will momentarily become blank before hiding.

UPDATE (8/25): Added transitionTimeout conditional statement.

[pkozlowski-opensource]

@merrihew Good catch! Would you be up to sending a pull request for this? We will need a test for this as well (so we don't accidentally remove this check in the future).

[merrihew]

@pkozlowski-opensource I'm happy to put together a pull request once I can write out the test.

I updated my code to use the transitionTimeout to properly time the content change. However, the code I copied has a note: // FIXME: this is a placeholder for a port of the transitions library.
Is the above code the correct way to handle this (for now) until the transitions library is implemented? It's a pretty nasty looking if/else but keeps it the closest match to the same statement in hide(). Thoughts?

[fxck]

Also wanted it on #559 was told it's duplicate of #590 which I believe was already implemented?