x11: fix support for dead keys

It seems to be required to pass a window to XCreateIC for receiving dead keys.

panda/src/x11display/x11GraphicsWindow.cxx

@@ -1081,10 +1081,8 @@ open_window() {
   XIM im = x11_pipe->get_im();
   _ic = nullptr;
   if (im) {
-    _ic = XCreateIC
-      (im,
-       XNInputStyle, XIMPreeditNothing | XIMStatusNothing,
-       nullptr);
+    _ic = XCreateIC(im, XNInputStyle, XIMPreeditNothing | XIMStatusNothing,
+                    XNClientWindow, _xwindow, nullptr);
     if (_ic == (XIC)nullptr) {
       x11display_cat.warning()
         << "Couldn't create input context.\n";