Merge branch 'ComboBox' of https://github.com/EdonGashi/MaterialDesignInXamlToolkit into EdonGashi-ComboBox

Author: ButchersBoy

MaterialDesignThemes.Wpf/HintProxyFabric.ComboBox.cs

@@ -16,7 +16,10 @@ private sealed class ComboBoxHintProxy : IHintProxy
             private readonly ComboBox _comboBox;
             private readonly TextChangedEventHandler _comboBoxTextChangedEventHandler;
 
-            public object Content => _comboBox.Text;
+            public object Content => _comboBox.IsEditable 
+                ? _comboBox.Text 
+                : _comboBox.SelectedItem != null ? " " : null;
+
             public bool IsLoaded => _comboBox.IsLoaded;
             public bool IsVisible => _comboBox.IsVisible;