Avoid unexcepted errors on "angucomplete" inputs

[RomainOliva]

I try to solve two problems in this PR.

1. Use case for the first problem:

• I enter a value for my input then I leave it
• I return in the input
• If I delete a character or modify the current value, an unexcepted required error message appears
• It disappears at the exit of the input.

Here is the solution:

• When writing in the input, for each key up, we enter in the condition line 291.
• The problem is for any user input the code call callOrAssign() method without parameters.
• When calling callOrAssign() input without parameters, the handleRequired(true) method is called and the field becomes invalid.
• What I add is a check, if the value of the input is empty we call callOrAssign() method without parameters to have an error, otherwise we send the value entered by the user to the callOfAssign method.
  In this way, the error no longer appears while the user writes (if the input is not empty).

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2. Use case of the second problems:

• I enter a value for my input then I leave it
• I return in the input
• If I completely empty the input an error will appear telling me that the field is mandatory (this is normal)
• But if I rewrite something without leaving the input, the error just stay

Here is the solution:

• When writing to the input, for each key up, we fill the last value of the input in the variable validState, the problem is that when we empty the input, the validStatevariable is""` and it never updated.
• So I modified the condition, to check if the validState is undefined and not if the variable is empty.
  In this way, if we empty the input, an error appears, but if we rewrite something, now the error disappears.

Here is the configuration of my angucomplete field:

this.brandOptions = {
      maxlength: '50',
      pause: '100',
      selectedObject: this.brandCallbackFunction.bind(this),
      localData: this.brands,
      searchFields: 'brand',
      titleField: 'brand',
      minlength: '1',
      textNoResults: false,
      textSearching: false,
      fieldRequired: true,
      fieldRequiredClass: 'brand',
      initialValue: this.newVariant.brand,
      inputName: 'brand',
      overrideSuggestions: true
    };