X wcfs: Do not fail if to-be-killed process exited by itself and was waited by its parent

wcfs/misc.go

@@ -586,10 +586,17 @@ func isProcessAlive(proc *os.Process) (_ bool, err error) {
 	// pid exists. Check if proc is not zombie
 	gproc, err := process.NewProcess(int32(proc.Pid))
 	if err != nil {
+		// XXX can fail even if ^^^ signal was ok (race)
 		return false, err
 	}
 	statusv, err := gproc.Status()
 	if err != nil {
+		// XXX isAlive pid804199: open /proc/804199/status: no such file or directory
+		//     ref:Zzj45iDT1E4PakvG@deca.navytux.spb.ru
+		var e syscall.Errno
+		if errors.As(err, &e) && e == syscall.ENOENT {
+			err = nil
+		}
 		return false, err
 	}
 	for _, status := range statusv {