title: Xamarin forms Label height issue
body: <p>I have a xaml page with Relative Layout > Grid(1row, 1col) + ActivityIndicator(1row, 1col)
  Grid has a scrollview which has a stacklayout and a button. 
  Stacklayout has a label with blank text and verticaloption set to FillAndExpand.</p>
  
  <p>On Page Appearing i am getting a value from a service and changing the label value. </p>
  
  <p><strong>Issue:</strong> As it is the label is rendering with height as 0, If i set label's default value as "something", Height of label is = 1 line and only 1 line of text is visible. If i set it to something like "\n\n\n\n\n multiple times" i am getting a scrollbar in page as expected, but the height of label is equal to \n\n\n count and not equal to the content that comes on appearing.</p>
  
  <p>What i can change so as to fix this problem? If code is required i can put it in here.</p>
  
  <pre><code>&lt;RelativeLayout&gt;
      &lt;Grid Padding="0" RelativeLayout.WidthConstraint="{ConstraintExpression Type=RelativeToParent, Property=Width}" RelativeLayout.HeightConstraint="{ConstraintExpression Type=RelativeToParent, Property=Height}"&gt;
          &lt;Grid.RowDefinitions&gt;
              &lt;RowDefinition Height="*" /&gt;
              &lt;RowDefinition Height="50" /&gt;
          &lt;/Grid.RowDefinitions&gt;
          &lt;Grid.ColumnDefinitions&gt;
              &lt;ColumnDefinition Width="*" /&gt;
          &lt;/Grid.ColumnDefinitions&gt;
          &lt;ScrollView x:Name="Scroller1" Grid.Row="0" Grid.Column="0" BackgroundColor="Aqua"&gt;
              &lt;StackLayout x:Name="Stack1" Padding="20,20,20,0" BackgroundColor="Fuchsia"&gt;
                  &lt;Label x:Name="Label1" VerticalOptions="FillAndExpand" BackgroundColor="Lime" Text="{Binding DisclaimerText}"  /&gt;
              &lt;/StackLayout&gt;
          &lt;/ScrollView&gt;
          &lt;Button Command="{Binding AgreeBtnTapCommand}" HeightRequest="50" Grid.Row="1" Grid.Column="0" BorderRadius="0" Text="Agree" TextColor="White" &gt;
          &lt;/Button&gt;
      &lt;/Grid&gt;
      &lt;controls:PageActivityIndicator RelativeLayout.WidthConstraint="{ConstraintExpression Type=RelativeToParent, Property=Width}" RelativeLayout.HeightConstraint="{ConstraintExpression Type=RelativeToParent, Property=Height}" IsVisible="{Binding IsBusy}" /&gt;
  &lt;/RelativeLayout&gt;
  </code></pre>