dumpling will report error when fallback to LOCK TABLE and upstream has no tables

[lance6716]

Bug Report

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1. Minimal reproduce step (Required)

[2022/10/27 14:49:47.503 +08:00] [ERROR] [main.go:77] ["dump failed error stack info"] [error="sql: : Error 1065: Query was empty"] [errorVerbose="Error 1065: Query was empty\nsql: \[ngithub.com/pingcap/tidb/dumpling/export.(*ConsistencyLockDumpingTables).Setup.func1\n\tgithub.com/pingcap/tidb/dumpling/export/consistency.go:151\ngithub.com/pingcap/tidb/br/pkg/utils.WithRetry\n\tgithub.com/pingcap/tidb/br/pkg/utils/retry.go:52\ngithub.com/pingcap/tidb/dumpling/export.(*ConsistencyLockDumpingTables).Setup\n\tgithub.com/pingcap/tidb/dumpling/export/consistency.go:136\ngithub.com/pingcap/tidb/dumpling/export.(*Dumper).Dump\n\tgithub.com/pingcap/tidb/dumpling/export/dump.go:157\nmain.main\n\t./main.go:74\nruntime.main\n\truntime/proc.go:250\nruntime.goexit\n\truntime/asm_arm64.s:1165](http://ngithub.com/pingcap/tidb/dumpling/export.(*ConsistencyLockDumpingTables).Setup.func1/n/tgithub.com/pingcap/tidb/dumpling/export/consistency.go:151/ngithub.com/pingcap/tidb/br/pkg/utils.WithRetry/n/tgithub.com/pingcap/tidb/br/pkg/utils/retry.go:52/ngithub.com/pingcap/tidb/dumpling/export.(*ConsistencyLockDumpingTables).Setup/n/tgithub.com/pingcap/tidb/dumpling/export/consistency.go:136/ngithub.com/pingcap/tidb/dumpling/export.(*Dumper).Dump/n/tgithub.com/pingcap/tidb/dumpling/export/dump.go:157/nmain.main/n/t./main.go:74/nruntime.main/n/truntime/proc.go:250/nruntime.goexit/n/truntime/asm_arm64.s:1165)"]

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

3. What did you see instead (Required)

4. What is your TiDB version? (Required)

[lance6716]

/cc @lichunzhu