Need a method to avoid the panic when os.Stdout is nil on windows platform.

[chenjie4255]

When the program is running as Windows system services, the os.stdout is nil. which results in a panic.

panic: nil passed instead of *os.File to NewColorable()

goroutine 1 [running]:
github.com/mattn/go-colorable.NewColorable(0x0)
	C:/Users/chen/go/pkg/mod/github.com/mattn/[email protected]/colorable_windows.go:104 +0x3d6
github.com/mattn/go-colorable.NewColorableStdout()
	C:/Users/chen/go/pkg/mod/github.com/mattn/[email protected]/colorable_windows.go:122 +0x25
github.com/fatih/color.init()
	C:/Users/chen/go/pkg/mod/github.com/fatih/[email protected]/color.go:27 +0x12d

link issue: mattn/go-colorable#76

Maybe we need a method to avoid calling the go-colorable.NewColorableStdout() when the os.Stdout is nil?