Update MaterialDesignTheme.TabControl.xaml (#2181)

Fix when TabStripPlacement = Top / Bottom , tabItem in headerPanel  not Horizontal

Author: stanley8615

MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.TabControl.xaml

@@ -374,8 +374,10 @@
                             <Setter TargetName="DividerRect" Property="HorizontalAlignment" Value="Stretch" />
                             <Setter TargetName="DividerRect" Property="Grid.ColumnSpan" Value="2" />
                             <Setter TargetName="DividerRect" Property="Grid.RowSpan" Value="1" />
-                            <Setter TargetName="HeaderPanel" Property="Rows" Value="0"/>
-                            <Setter TargetName="HeaderPanel" Property="Columns" Value="1"/>
+                            <Setter TargetName="HeaderPanel" Property="Rows" Value="1"/>
+                            <Setter TargetName="HeaderPanel" Property="Columns" Value="0"/>
+                            <Setter TargetName="HeaderPanel" Property="HorizontalAlignment" Value="Left"/>
+                            <Setter TargetName="HeaderPanel" Property="VerticalAlignment" Value="Stretch"/>
                         </Trigger>
                         <Trigger Property="TabStripPlacement" Value="Bottom">
                             <Setter Property="wpf:ShadowAssist.ShadowEdges" Value="Top"/>
@@ -387,8 +389,10 @@
                             <Setter TargetName="DividerRect" Property="HorizontalAlignment" Value="Stretch" />
                             <Setter TargetName="DividerRect" Property="Grid.ColumnSpan" Value="2" />
                             <Setter TargetName="DividerRect" Property="Grid.RowSpan" Value="1" />
-                            <Setter TargetName="HeaderPanel" Property="Rows" Value="0"/>
-                            <Setter TargetName="HeaderPanel" Property="Columns" Value="1"/>
+                            <Setter TargetName="HeaderPanel" Property="Rows" Value="1"/>
+                            <Setter TargetName="HeaderPanel" Property="Columns" Value="0"/>
+                            <Setter TargetName="HeaderPanel" Property="HorizontalAlignment" Value="Left"/>
+                            <Setter TargetName="HeaderPanel" Property="VerticalAlignment" Value="Stretch"/>
                         </Trigger>
                         <Trigger Property="TabStripPlacement" Value="Right">
                             <Setter Property="wpf:ShadowAssist.ShadowEdges" Value="Left"/>
@@ -401,4 +405,4 @@
             </Setter.Value>
         </Setter>
     </Style>
-</ResourceDictionary>
+</ResourceDictionary>