title: Material Date Picker Validation not working with FormBuilder.patchValue()
body: <p>I have a form that requires a user to enter a date, the submit button is greyed out until they do so. This works perfectly until I have to edit the form. For some reason the validation isn't picking up my timestamp that populates the date field when I use <code>FormBuilder</code>'s <code>patchValue()</code> method like so:</p>
  
  <p>In my page constructor I build my form (other fields removed for brevity):</p>
  
  <pre><code>this.submitForm = this.formBuilder.group({
    submissionReleaseDate: ['', Validators.required]
  });
  </code></pre>
  
  <p>Then in my <code>ngOnInit()</code> I query to get the releaseDate from my database and then run:</p>
  
  <pre><code>    this.submitForm.patchValue({
        submissionReleaseDate: moment.unix(this.submission.submissionReleaseDate).utc(),
      }) 
  </code></pre>
  
  <p>All the other fields from my form are validated (when checking the classes added by angular I see ng-valid) except for the date field (where the class remains ng-invalid) until I type a character into that field.</p>
  
  <p>Here's what it looks like when I load the edit page, as you can see the submit button is greyed out even though the fields are populated:</p>
  
  <p><a href="https://i.stack.imgur.com/9ROdU.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/9ROdU.png" alt="enter image description here"></a></p>
  
  <p>Here's my material date picker html:</p>
  
  <pre><code>&lt;input matInput [min]="date" formControlName="submissionReleaseDate" [matDatepicker]="picker" placeholder="Choose a date"&gt;
  &lt;mat-datepicker-toggle matSuffix [for]="picker"&gt;&lt;/mat-datepicker-toggle&gt;
  &lt;mat-datepicker #picker&gt;&lt;/mat-datepicker&gt;
  </code></pre>
  
  <p>And my <code>module.ts</code> for that page:</p>
  
  <pre><code>@NgModule({
    imports: [
      CommonModule,
      FormsModule,
      ReactiveFormsModule,
      IonicModule,
      NgAisModule,
      MatDatepickerModule,
      MatMomentDateModule,
      MatNativeDateModule,
      RouterModule.forChild(routes),
    ],
    providers: [
      {provide: DateAdapter, useClass: MomentDateAdapter, deps: [MAT_DATE_LOCALE]},
      {provide: MAT_DATE_FORMATS, useValue: MAT_MOMENT_DATE_FORMATS},
      { provide: MAT_MOMENT_DATE_ADAPTER_OPTIONS, useValue: { useUtc: true } }
    ],
    declarations: [SubmitPage]
  })
  </code></pre>