Fixed the resizing deadlock.

stdwndclass_windows.go

@@ -51,10 +51,13 @@ func stdWndProc(s *sysData) func(hwnd _HWND, uMsg uint32, wParam _WPARAM, lParam
 				if r1 == 0 {
 					panic("GetClientRect failed: " + err.Error())
 				}
+				// run the resize in a goroutine, since the WndProc is being run on uitask
+				go func() {
 					err = s.resize(int(r.Left), int(r.Top), int(r.Right), int(r.Bottom))
 					if err != nil {
 						panic("child resize failed: " + err.Error())
 					}
+				}()
 			}
 			return 0
 		case _WM_CLOSE: