Nested union types fail equality check

``` js
/** @constructor @template T */
function EventType(){}

/**
* @param {string|!EventType} a
* @param {!EventType} b
* @return {boolean}
*/
function compare(a, b) {
return a === b;
}
```

``` js
input0:10: WARNING - condition always evaluates to false
left : (EventType<(boolean|number)>|string)
right: EventType
return a === b;
^
```

The (obviously-incorrect) error only happens if both `|`s are present.

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