Floating label on ion-datetime always floats if it's in a formGroup or has ngModel

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Ionic version: (check one with "x")
[x] 3.x

I'm submitting a ... (check one with "x")
[x] bug report

Current behavior:
A floating label on <ion-datetime> always floats above the input, even if no date is selected. This happens if the ion-datetime has ngModel or is in a formGroup. If it's neither, then it only floats when a date is selected (but then it becomes useless, as you can't actually get the value).

Expected behavior:
The floating label should only float when a date is selected.

Steps to reproduce:
See this plunker

Related code:
Other information:
I think the issue is in the hasValue() method in base-input.ts. It returns true if the datetime has the "empty" date (which is just {}). Either ion-datetime should have null or undefined value until a date is selected, or it could override hasValue() and return false if the value is {}.

Ionic info:

> ionic info

Your system information:

 ordova CLI: 7.0.0
Ionic Framework Version: 3.1.1
Ionic CLI Version: 2.2.3
Ionic App Lib Version: 2.2.1
Ionic App Scripts Version: 1.3.6
ios-deploy version: Not installed
ios-sim version: Not installed
OS: Windows 10
Node Version: v6.10.3
Xcode version: Not installed```

[gandrade74]

Same problem here.

[ionitron-bot]

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