Handle textless messages differently, bringing Node into parity with .NET

[v-kydela]

Fixes microsoft/botbuilder-dotnet#1349

Description

While there wasn't necessarily a bug in this repo, there was potential for LuisRecognizer to make a needless call to a LUIS endpoint when an utterance was empty. This PR gets the behavior of LuisRecognizer to match a recent V4 .NET PR which in turn is based off of V3 .NET. Now the recognize function will check if an utterance is empty and then create a fake result instead of getting a result from the endpoint in that case.

Specific Changes

• LuisRecognizer.recognize now creates a RecognizerResult with a blank intent if the activity's text is null or whitespace
• The EmptyText.json test in luisRecognizer.test.js now checks the actual RecognizerResult instead of just the topIntent function because topIntent converts the empty intent to None

Testing

The EmptyText test has been modified to fit the new behavior.

[coveralls]

Pull Request Test Coverage Report for Build #2230

• 6 of 6 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.02%) to 85.729%

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Totals
Change from base Build #2229:	0.02%
Covered Lines:	3260
Relevant Lines:	3665

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💛 - Coveralls

[cleemullins]

This is great, but could you:

1. Do the linting changes, and only the linting changes, in a PR.
2. Once that's merged in, make the bug fix.

Looking through this PR I can't tell what's new and what's just a linting change, as the changeset is complex.

[v-kydela]

@cleemullins - All right, I went ahead and did the linting in its own PR and requested you as a reviewer: #867

I must have idly auto-formatted the document without realizing how much actually got changed

[cleemullins]

@v-kydela When I look at the Diff of this PR, I still see all the linting changes. I did merge in the separate PR with those changes earlier this evening, so I'm surprised to see them still in this PR.

Can you take a look?

[v-kydela]

@cleemullins - It looks to me like your merge successfully removed the linting changes from this PR:

Can you look again? Maybe clear your cache or something? If you need me to change this PR then I could try a rebase but that could get messy. Then of course the last resort would be to discard this PR and just create a new one.