Fix index out of range

[yusuke-koyoshi]

Fixed a bug where the index was out of range when the input string was short.

func main() {
	if len(os.Args) == 1 {
		_, _ = fmt.Fprintf(os.Stderr, "usage: %s string1 [string2]...\n", os.Args[0])
		os.Exit(1)
	}

	fmt.Printf("%s\n", unique_string.GenerateUniqueString(os.Args[1:]...))
}

$ ./go-azure-unique-string a a
panic: runtime error: index out of range [3] with length 3

goroutine 1 [running]:
github.com/cloud-maker-ai/go-unique-string.murmurHash64({0x14000090020?, 0x102f29088?, 0x2?})
	/Users/yusuke.koyoshi/go/pkg/mod/github.com/cloud-maker-ai/go-unique-string@v0.0.0-20221215222937-c55128876647/unique_string.go:56 +0x304
github.com/cloud-maker-ai/go-unique-string.GenerateUniqueString({0x140000a0070?, 0x0?, 0x1400005e738?})
	/Users/yusuke.koyoshi/go/pkg/mod/github.com/cloud-maker-ai/go-unique-string@v0.0.0-20221215222937-c55128876647/unique_string.go:113 +0x44
main.main()
	/Users/yusuke.koyoshi/ghq/test/go-azure-unique-string/main.go:18 +0x54

[berlincount]

I'd also need this fix to be applied, running into the same problem ...