websocket: Do not try to send frames on closed sockets
websocket: Do not try to send frames on closed sockets

[E 2015/04/05 20:22:07] [iostream.lua] Error in callback /turbo/iostream.lua:1017: Socket operation on closed stream.. Closing socket.
stack traceback:
	/turbo/iostream.lua:531: in function </turbo/iostream.lua:528>
	[C]: in function 'error'
	/turbo/iostream.lua:1017: in function '_check_closed'
	/turbo/iostream.lua:291: in function 'write'
	/turbo/websocket.lua:285: in function '_send_frame'
	/turbo/websocket.lua:186: in function 'close'
	/turbo/websocket.lua:535: in function '_handle_opcode'
	/turbo/websocket.lua:520: in function '_frame_payload'
	/turbo/websocket.lua:271: in function </turbo/websocket.lua:269>
	[C]: in function 'xpcall'
	/turbo/iostream.lua:544: in function </turbo/iostream.lua:534>
	[C]: in function 'xpcall'
	/turbo/ioloop.lua:537: in function </turbo/ioloop.lua:536>

Signed-off-by: Petr Štetiar <f0d4d86d9c7002e67e6ae7bb5596bc0afa7b4c3a@true.cz>

luastoned/turbo,YuanPeir-Chen/turbo-support-mipsel,luastoned/turbo,zcsteele/turbo,kernelsauce/turbo,ddysher/turbo,YuanPeir-Chen/turbo-support-mipsel,mniestroj/turbo,ddysher/turbo,zcsteele/turbo