make sure unlock safe even if listeners panic (#383)

* make sure unlock safe even if listeners panic

* fix #378

* fix #378

core/proc/shutdown+polyfill.go

@@ -4,10 +4,12 @@ package proc
 
 import "time"
 
+// AddShutdownListener returns fn itself on windows, lets callers call fn on their own.
 func AddShutdownListener(fn func()) func() {
 	return fn
 }
 
+// AddWrapUpListener returns fn itself on windows, lets callers call fn on their own.
 func AddWrapUpListener(fn func()) func() {
 	return fn
 }