Fail to parse an index key

[JaySon-Huang]

>  mok 748000000000001dffb25f698000000000ff00000c0380000000ff245c32c103800000ff0000000006038000ff00006818d60803d8ff00000008c904c300fe
panic: runtime error: index out of range [-8]

goroutine 1 [running]:
github.com/pingcap/tidb/types.DecimalBinSize(...)
	/Users/jayson/go/pkg/mod/github.com/pingcap/tidb@v1.1.0-beta.0.20220610072431-5d4745e9d415/types/mydecimal.go:1486
github.com/pingcap/tidb/types.(*MyDecimal).FromBin(0x14000511968?, {0x1400013c764?, 0x19d8?, 0x1020fdb28?}, 0x1020f05b8?, 0x18?)
	/Users/jayson/go/pkg/mod/github.com/pingcap/tidb@v1.1.0-beta.0.20220610072431-5d4745e9d415/types/mydecimal.go:1404 +0x798
github.com/pingcap/tidb/util/codec.DecodeDecimal({0x1400013c764, 0x10, 0x1c})
	/Users/jayson/go/pkg/mod/github.com/pingcap/tidb@v1.1.0-beta.0.20220610072431-5d4745e9d415/util/codec/decimal.go:59 +0x118
github.com/pingcap/tidb/util/codec.DecodeOne({0x1400013c761?, 0x1400013a160?, 0x14000511b48?})
	/Users/jayson/go/pkg/mod/github.com/pingcap/tidb@v1.1.0-beta.0.20220610072431-5d4745e9d415/util/codec/codec.go:833 +0x1d8
main.DecodeIndexValues(0x18?)
	/Users/jayson/Projects/myproj/mok/rules.go:133 +0xcc
main.(*Node).Expand(0x140000c68c0)
	/Users/jayson/Projects/myproj/mok/mok.go:68 +0x6c
main.(*Node).Expand(0x140000c67c0)
	/Users/jayson/Projects/myproj/mok/mok.go:70 +0xa4
main.(*Node).Expand(0x140000c6580)
	/Users/jayson/Projects/myproj/mok/mok.go:70 +0xa4
main.(*Node).Expand(0x140000c6540)
	/Users/jayson/Projects/myproj/mok/mok.go:70 +0xa4
main.(*Node).Expand(0x140000c6500)
	/Users/jayson/Projects/myproj/mok/mok.go:70 +0xa4
main.main()
	/Users/jayson/Projects/myproj/mok/main.go:41 +0x654

But this key can be parse by tidb_decode_key

TiDB root@10.2.12.81:test> select tidb_decode_key('748000000000001dffb25f698000000000ff00000c0380000000ff245c32c103800000ff0000000006038000ff00006818d60803d8ff00000008c904c300fe')
+---------------------------------------------------------------------------------------------------------------------------------------------------+
| tidb_decode_key('748000000000001dffb25f698000000000ff00000c0380000000ff245c32c103800000ff0000000006038000ff00006818d60803d8ff00000008c904c300fe') |
+---------------------------------------------------------------------------------------------------------------------------------------------------+
| {"index_id":12,"index_vals":"610022081, 6, 1746458120, 6341068275485050051","table_id":7602}                                                      |
+---------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set
Time: 0.011s
TiDB root@10.2.12.81:test> select tidb_version() \G;
***************************[ 1. row ]***************************
tidb_version() | Release Version: v9.0.0-alpha-386-gc902ad1
Edition: Community
Git Commit Hash: c902ad1f4cb7172f04af4c414400da2e3176a88f
Git Branch: HEAD
UTC Build Time: 2025-03-10 20:49:28
GoVersion: go1.23.7
Race Enabled: false
Check Table Before Drop: false
Store: tikv