CompilePath panics when it should return an error

[M0rdecay]

Hello!

Trying your library, I ran into this situation - CompilePath function panics when it should return an error. Perhaps I am doing something wrong? Please, help!

	xmlDocument := etree.NewDocument()
	xmlDocument.ReadFromString(xml)
	
	path, err := etree.CompilePath("/][") // <- Wrong query here
	if err != nil {
		fmt.Println(err)
		return
	}

	root := xmlDocument.FindElementsPath(path)

Output:

panic: runtime error: index out of range [-1]

goroutine 1 [running]:
github.com/beevik/etree.(*compiler).parseSegment(0xc000068e98, 0x4dd524, 0x2, 0x0, 0x0, 0x0, 0x0, 0x0)
	/tmp/gopath622730673/pkg/mod/github.com/beevik/[email protected]/path.go:258 +0x2d7
github.com/beevik/etree.(*compiler).parsePath(0xc000068e98, 0x4dd523, 0x3, 0x5ba000, 0x0, 0x590)
	/tmp/gopath622730673/pkg/mod/github.com/beevik/[email protected]/path.go:226 +0x165
github.com/beevik/etree.CompilePath(0x4dd523, 0x3, 0x590, 0x0, 0x0, 0x4b19f1, 0x4c4360)
	/tmp/gopath622730673/pkg/mod/github.com/beevik/[email protected]/path.go:99 +0x4b
main.main()
	/tmp/sandbox091201306/prog.go:50 +0x70

Code example - https://play.golang.org/p/kO5V_6Q_mCk