fix(FormlyFormController): Fix validateOnModelChange not firing with promise change #523

[Rybbow]

What

In FormlyFormController in function validateFormControl variable validate was invoked with "undefined" this if the function was called with a promise.

Why

It's a bug.

How

Used a closure and apply() to ensure validate() will be called with formController as this.

For issue #523

Checklist:

• [X] Follows the commit message conventions
• [X] Is rebased with master
• [X] Is only one (maybe two) commits

Fixes validate being called with undefined this variable scope.

Closes #523

[GitCop]

There were the following issues with your Pull Request

• Commit: ed1fcfcda8017dbcf03a0fd0b56040535b511bec
  • Your subject line is longer than 72 characters

Guidelines are available at https://github.com/formly-js/angular-formly/blob/master/CONTRIBUTING.md

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[codecov-io]

Current coverage is 95.93% (diff: 100%)

Merging #728 into master will not change coverage

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  Hits           1133       1133          
  Misses           48         48          
  Partials          0          0          

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[kentcdodds]

Could someone from @angular-formly-collaborators review and merge this?

[kentcdodds]

Sorry, bad @ mention. Someone from @formly-js/angular-formly-collaborators please review and merge this. Thanks.