directly return the value if its a string in DmnComboBox

Author: JoshElias

RazorUI/Input/DmnComboBox.razor.cs

@@ -59,6 +59,7 @@ public object GetPropertyValue(object obj, string propertyName)
     }
 
     private string GetTextValue(object obj) {
+        if(obj is string) return obj as string;
         return GetPropertyValue(obj, TextFieldName).ToString();
     }