A panic in lexer.go: [runtime error: index out of range]

[MyLGG]

Hello
I find a bug when using lexer.Lex(). Here is the poc

import (
	"github.com/z7zmey/php-parser/pkg/conf"
	"github.com/z7zmey/php-parser/pkg/version"
        "testing"
        "gotest.tools/assert"
)

func TestCrash(t *testing.T) {
	src := "=<?i<F<o�Q<}!45"
	expected := []string{
		token.T_START_HEREDOC.String(),
	}
	config := conf.Config{
		Version: &version.Version{
			Major: 7,
			Minor: 4,
		},
	}
	lexer := NewLexer([]byte(src), config)
	actual := []string{}
	for {
		tkn := lexer.Lex()
		if tkn.ID == 0 {
			break
		}
		actual = append(actual, tkn.ID.String())
	}
	assert.DeepEqual(t, expected, actual)
}

The stack information is this:

goroutine 33 [running]:
testing.tRunner.func1.2(0x67c4e0, 0xc000228060)
        /home/lyf/.local/go/src/testing/testing.go:1143 +0x332
testing.tRunner.func1(0xc000102480)
        /home/lyf/.local/go/src/testing/testing.go:1146 +0x4b6
panic(0x67c4e0, 0xc000228060)
        /home/lyf/.local/go/src/runtime/panic.go:965 +0x1b9
github.com/z7zmey/php-parser/internal/scanner.(*Lexer).ret(0xc00011aeb8, 0x1)
        /home/lyf/workspace/gowork/src/fuzzTestee_lyf/projects/php-parser/internal/scanner/lexer.go:214 +0x65
github.com/z7zmey/php-parser/internal/scanner.(*Lexer).Lex(0xc00010deb8, 0xc00012a376)
        /home/lyf/workspace/gowork/src/fuzzTestee_lyf/projects/php-parser/internal/scanner/scanner.go:3789 +0x19971
github.com/z7zmey/php-parser/internal/scanner.TestHereDocUnclosed(0xc000102480)
        /home/lyf/workspace/gowork/src/fuzzTestee_lyf/projects/php-parser/internal/scanner/scanner_test.go:1115 +0x36e
testing.tRunner(0xc000102480, 0x6a0a30)
        /home/lyf/.local/go/src/testing/testing.go:1193 +0xef
created by testing.(*T).Run
        /home/lyf/.local/go/src/testing/testing.go:1238 +0x2b3

[Milos Colakovic]

It looks like the panic-causing code can be boiled down to <?}