bug: when parsing formula in a list, panic: interface conversion: interface {} is nil, not *mathjax.mathBlockData

[pluveto]

Reproduce example:

package main

import (
	"bytes"
	"fmt"

	mathjax "github.com/litao91/goldmark-mathjax"
	"github.com/yuin/goldmark"
	"github.com/yuin/goldmark/parser"
	"github.com/yuin/goldmark/renderer/html"
)

func main() {
	md := goldmark.New(
		goldmark.WithExtensions(mathjax.MathJax),
		goldmark.WithParserOptions(
			parser.WithAutoHeadingID(),
		),
		goldmark.WithRendererOptions(
			html.WithHardWraps(),
			html.WithXHTML(),
		),
	)

	// todo more control on the parsing process
	var html bytes.Buffer
	mdContent := []byte(`

- 现在考虑整数 $n$

	$$
	n = p_1 p_2 \ldots p_k = q_1 q_2 \ldots q_l
	$$


`)
	if err := md.Convert(mdContent, &html); err != nil {
		fmt.Println(err)
	}
	fmt.Println(html.String())
}

Result:

$ go run main.go
panic: interface conversion: interface {} is nil, not *mathjax.mathBlockData

goroutine 1 [running]:
github.com/litao91/goldmark-mathjax.(*mathJaxBlockParser).Continue(0xc0002005b0?, {0x616678, 0xc000197280}, {0x615d38, 0xc0002005b0}, {0x615f38, 0xc000200690})
        /home/pluveto/go/pkg/mod/github.com/litao91/[email protected]/block.go:47 +0x3b4
github.com/yuin/goldmark/parser.(*parser).parseBlocks(0xc00020b508, {0x616ad8, 0xc000197080}, {0x615d38, 0xc0002005b0}, {0x615f38, 0xc000200690})
        /home/pluveto/go/pkg/mod/github.com/yuin/[email protected]/parser/parser.go:1063 +0x5b9
github.com/yuin/goldmark/parser.(*parser).Parse(0xc00020b508, {0x615d38, 0xc0002005b0}, {0x0, 0x0, 0x40ce45?})
        /home/pluveto/go/pkg/mod/github.com/yuin/[email protected]/parser/parser.go:848 +0x14b
github.com/yuin/goldmark.(*markdown).Convert(0xc0001f42c0, {0xc000218000, 0x53, 0x53}, {0x6149a8, 0xc00012b080}, {0x0, 0x0, 0x0})
        /home/pluveto/go/pkg/mod/github.com/yuin/[email protected]/markdown.go:116 +0xce
main.main()
        /home/pluveto/repo/blog-ws/test/main.go:37 +0x347
exit status 2