title: Form validation not working in mdDialog
body: <p>I have this simple working <code>form</code>, but when I put this in a <code>$mdDialog</code> it doesn't disable the submit button anymore... it basically ignores the <code>networktypeForm.$invalid</code> Is this common or is there a fix for this?</p>
  
  <pre><code>&lt;form name="networktypeForm" ng-submit="add()" novalidate role="form"&gt;
      &lt;div class="md-dialog-content"&gt;
        &lt;md-input-container md-no-float flex&gt;
          &lt;label&gt;Element type&lt;/label&gt;
          &lt;input flex ng-model="type" name="networktype" type="text" required=""&gt;
          &lt;div ng-messages="networktypeForm.networktype.$error"&gt;
            &lt;div ng-message="required"&gt;This is required&lt;/div&gt;
          &lt;/div&gt;
        &lt;/md-input-container&gt;
      &lt;/div&gt;
      &lt;md-dialog-actions layout="row"&gt;
        &lt;md-button type="submit" class="md-primary md-raised" ng-disabled="networktypeForm.$invalid"&gt;
          Add
        &lt;/md-button&gt;
      &lt;/md-dialog-actions&gt;
    &lt;/form&gt;
  </code></pre>