Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. run backup and terminate it.
2. run backup again.

2. What did you expect to see? (Required)

success

3. What did you see instead (Required)

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0]
goroutine 1 [running]:
github.com/pingcap/tidb/br/pkg/backup.(*Schemas).BackupSchemas
        /.../tidb/br/pkg/backup/schema.go:119 +0x7a0

4. What is your TiDB version? (Required)

master