fix to execas.Command

[zerobyted]

cm := execas.Command("notepad")
cm.Username = "gola"
cm.Password = "loga"
err := cm.Start()
if err != nil {
    fmt.Println("err", err.Error())
}

panics after start process

ox/syscallex/exec_windows.go

Lines 254 to 255 in 32d876f

	attr.Sys.ThreadHandle = syscall.Handle(pi.Thread)
	attr.Sys.ProcessHandle = syscall.Handle(pi.Process)

attr.Sys == nil because there no update after

ox/syscallex/exec_windows.go

Lines 138 to 141 in 32d876f

	sys := attr.Sys
	if sys == nil {
	sys = &zeroSysProcAttr
	}

changing attr.Sys... to sys... do the deal.