border attribute must be initialized

so that we can run the client without window forwarding enabled

xpra/client/gtk3/client_base.py

@@ -141,6 +141,7 @@ def __init__(self):
         self.gl_max_viewport_dims = 0, 0
         self.gl_texture_size_limit = 0
         self._cursors = weakref.WeakKeyDictionary()
+        self.border_str = "no"
         # frame request hidden window:
         self.frame_request_window = None
         # group leader bits:
@@ -159,6 +160,7 @@ def __init__(self):
     def init(self, opts) -> None:
         GObjectXpraClient.init(self, opts)
         UIXpraClient.init(self, opts)
+        self.border_str = opts.border
 
     def setup_frame_request_windows(self) -> None:
         # query the window manager to get the frame size: