For an invalid input field, only make the label red when it's floating

[calebegg]

Fixes issue #1928. (See that issue for details).

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[calebegg]

I work at Google, so I don't think I need to separately sign the CLA. I updated my email address on github to be my @google.com address -- do I need to do anything else?

[ThomasBurleson]

@calebegg - I think you are good. Thx for this PR... and thx for contributing.

[calebegg]

No problem. :-)