fix(autocomplete): panel not closing on IE when selecting an option with an empty string display value

[crisbeto]

Fixes the autocomplete panel reopening on IE11 when the user selects an option whose display value is an empty string.

Fixes #9479.

[jelbourn]

LGTM

[jelbourn]

It's possible that checking activeElement may start to make some tests fail (if people are faking input events). We'll see how the presubmit goes.

[crisbeto]

The activeElement check was already there, this only introduces the check for the value.

[tinayuangao]

@crisbeto please rebase. Thanks!

[crisbeto]

Rebased.

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