should disable the remove and dupliate button if there is no selection

Author: heartacker

src/Views/Preferences.axaml

@@ -605,13 +605,15 @@
                   <Button Grid.Column="1"
                           Classes="icon_button"
                           Width="28" Height="28"
-                          Click="OnRemoveSelectedCustomAction">
+                          Click="OnRemoveSelectedCustomAction"
+                          IsEnabled="{Binding #ThisControl.SelectedCustomAction, Converter={x:Static ObjectConverters.IsNotNull}}">
                     <Path Width="14" Height="14" Data="{StaticResource Icons.Minus}"/>
                   </Button>
                   <Button Grid.Column="2"
                           Classes="icon_button"
                           Width="28" Height="28"
-                          Click="OnDuplicateSelectedCustomAction">
+                          Click="OnDuplicateSelectedCustomAction"
+                          IsEnabled="{Binding #ThisControl.SelectedCustomAction, Converter={x:Static ObjectConverters.IsNotNull}}">
                     <Path Width="14" Height="14" Data="{StaticResource Icons.Copy}"/>
                   </Button>
                   <Button Grid.Column="4"

src/Views/RepositoryConfigure.axaml

@@ -434,13 +434,15 @@
                 <Button Grid.Column="1"
                         Classes="icon_button"
                         Width="28" Height="28"
-                        Command="{Binding RemoveSelectedCustomAction}">
+                        Command="{Binding RemoveSelectedCustomAction}"
+                        IsEnabled="{Binding SelectedCustomAction, Converter={x:Static ObjectConverters.IsNotNull}}">
                   <Path Width="14" Height="14" Data="{StaticResource Icons.Minus}"/>
                 </Button>
                 <Button Grid.Column="2"
                         Classes="icon_button"
                         Width="28" Height="28"
-                        Command="{Binding DuplicateSelectedCustomAction}">
+                        Command="{Binding DuplicateSelectedCustomAction}"
+                        IsEnabled="{Binding SelectedCustomAction, Converter={x:Static ObjectConverters.IsNotNull}}">
                   <Path Width="14" Height="14" Data="{StaticResource Icons.Copy}"/>
                 </Button>
                 <Button Grid.Column="4"