Describe the bug

Hey, thanks a lot for creating and maintaining this library. I have started exploring this library as part of extending a snapshot testing library that I have https://github.com/gkampitakis/go-snaps and I want to support YAML snapshots. I was looking into yaml.PathString and when I pass a path with starting with a dot it panics.

Also apart from the README.md I can't find any examples or documentation for the valid yaml path syntax, maybe I missed it.

To Reproduce

package main

import (
	"github.com/goccy/go-yaml"
)

func main() {
	yaml.PathString(".address")
}


/**
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x2 addr=0x20 pc=0x104765254]

goroutine 1 [running]:
github.com/goccy/go-yaml.(*PathBuilder).child(...)
*/

Please provide a minimum yaml content that can be reproduced.
We are more than happy to use Go Playground

Expected behavior

I would expect an error if this is invalid path.

Version Variables

• Go version: 1.23.2
• go-yaml's Version: v1.15.10

Additional context
Add any other context about the problem here.