Merge pull request #3528 from Symbai/comboboxHeightFix

Fix Combobox height if no item is selected v2

src/Avalonia.Themes.Default/ComboBox.xaml

@@ -4,6 +4,7 @@
     <Setter Property="BorderBrush" Value="{DynamicResource ThemeBorderMidBrush}"/>
     <Setter Property="BorderThickness" Value="{DynamicResource ThemeBorderThickness}"/>
     <Setter Property="Padding" Value="4"/>
+    <Setter Property="MinHeight" Value="20"/>
     <Setter Property="Template">
       <ControlTemplate>
         <Border Name="border"
@@ -40,14 +41,14 @@
                    StaysOpen="False">
               <Border BorderBrush="{DynamicResource ThemeBorderMidBrush}"
                       BorderThickness="1">
-                  <ScrollViewer>
-                      <ItemsPresenter Name="PART_ItemsPresenter"
-                                      Items="{TemplateBinding Items}"
-                                      ItemsPanel="{TemplateBinding ItemsPanel}"
-                                      ItemTemplate="{TemplateBinding ItemTemplate}"
-                                      VirtualizationMode="{TemplateBinding VirtualizationMode}"
+                <ScrollViewer>
+                  <ItemsPresenter Name="PART_ItemsPresenter"
+                                  Items="{TemplateBinding Items}"
+                                  ItemsPanel="{TemplateBinding ItemsPanel}"
+                                  ItemTemplate="{TemplateBinding ItemTemplate}"
+                                  VirtualizationMode="{TemplateBinding VirtualizationMode}"
                               />
-                  </ScrollViewer>
+                </ScrollViewer>
               </Border>
             </Popup>
           </Grid>
@@ -58,7 +59,7 @@
   <Style Selector="ComboBox:pointerover /template/ Border#border">
     <Setter Property="BorderBrush" Value="{DynamicResource ThemeBorderHighBrush}"/>
   </Style>
-    <Style Selector="ComboBox:disabled /template/ Border#border">
-        <Setter Property="Opacity" Value="{DynamicResource ThemeDisabledOpacity}" />
-    </Style>
+  <Style Selector="ComboBox:disabled /template/ Border#border">
+    <Setter Property="Opacity" Value="{DynamicResource ThemeDisabledOpacity}" />
+  </Style>
 </Styles>