fix:Index out of bounds.

src/Ursa/Controls/PathPicker/PathPicker.cs

@@ -139,11 +139,14 @@ public class PathPicker : TemplatedControl
         {
             _twoConvertLock = true;
             var stringBuilder = new StringBuilder();
+            if (SelectedPaths.Count != 0)
+            {
                 stringBuilder.Append(SelectedPaths[0]);
                 foreach (var item in SelectedPaths.Skip(1))
                 {
                     stringBuilder.AppendLine(item);
                 }
+            }
 
             SelectedPathsText = stringBuilder.ToString();
             _twoConvertLock = false;