fix space key input on x11

src/Avalonia.X11/X11Window.cs

@@ -731,7 +731,7 @@ namespace Avalonia.X11
         void DispatchInput(RawInputEventArgs args)
         {
             Input?.Invoke(args);
-            if (!args.Handled && args is RawKeyEventArgsWithText text && !string.IsNullOrWhiteSpace(text.Text))
+            if (!args.Handled && args is RawKeyEventArgsWithText text && !string.IsNullOrEmpty(text.Text))
                 Input?.Invoke(new RawTextInputEventArgs(_keyboard, args.Timestamp, _inputRoot, text.Text));
         }