[Wisp] Keep aligning Socket.isConnected() with the normal OpenJDK returning result for ServerSocket.accept()

[zhengxiaolinX]

Summary: Same as #438: we have another path ServerSocket.accept() to cover.

Test Plan: ServerSocketConnectionTest.java

Reviewed-by: D-D-H, yuleil

Issue: #437

[zhengxiaolinX]

The failed test is not related to this patch. Going to merge this first and we will look at it afterwards.