panic: send on closed channel

[wubie052]

version:2.11.1 --> 2,11,14
latest and correct version：2.11.11

hi，commit(#447) seems to have triggered a new error. Now, when I use Ctrl+C to close the application in Windows, an error message appears: panic: send on closed channel.

Reason:Usually, signal channels are registered by signal.notify and should not be manually closed.
signal.Notify doesn't care whether the channel is closed or not, but if you range this channel elsewhere, it will cause an early exit.
A more reasonable approach is: Do not close the signal channel unless you have full control over its lifecycle.

close(app.sgChan)

Now, when I repeatedly execute Ctrl+C in Windows to close an application (note that a single input of Ctrl+C does not result in an error, but in version 2.11.1, even multiple inputs of Ctrl+C can correctly close it), an error occurs:

panic: send on closed channel
goroutine 14 [running]:
os/signal.process({0x22c2338, 0x2f061f0})
C:/Users/Admin/.g/go/src/os/signal/signal.go:245 +0x1a5
os/signal.loop()
C:/Users/Admin/.g/go/src/os/signal/signal_unix.go:23 +0x29
created by os/signal.Notify.func1.1 in goroutine 1
C:/Users/Admin/.g/go/src/os/signal/signal.go:151 +0x1f
exit status 2

[wubie052]

@hspedro @rsafonseca