fix #151 Add context menu for programs

Wox/Converters/StringNullOrEmptyToVisibilityConverter.cs

@@ -1,6 +1,8 @@
 using System;
+using System.Collections.Generic;
 using System.Globalization;
 using System.Windows;
+using Wox.Plugin;
 
 namespace Wox.Converters
 {
@@ -21,4 +23,23 @@ namespace Wox.Converters
             return this;
         }
     }
+
+    public class ContextMenuEmptyToWidthConverter : ConvertorBase<ContextMenuEmptyToWidthConverter>
+    {
+        public override object Convert(object value, Type targetType, object parameter, CultureInfo culture)
+        {
+            List<Result> results = value as List<Result>;
+            return results == null || results.Count == 0 ? 0 : 17;
+        }
+
+        public override object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
+        {
+            return null;
+        }
+
+        public override object ProvideValue(IServiceProvider serviceProvider)
+        {
+            return this;
+        }
+    }
 }