DM-worker panic when query-status or query-error

[csuzhangxc]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do? If possible, provide a recipe for reproducing the error.

query-error.

2. What did you expect to see?

return anything.

3. What did you see instead?

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x58 pc=0x1867bff]

goroutine 17712 [running]:
github.com/pingcap/dm/dm/worker.(*Worker).Error(0xc00012a000, 0xc002c95250, 0x9, 0x114, 0x0, 0x0)
	/home/jenkins/agent/workspace/build_dm_master/go/src/github.com/pingcap/dm/dm/worker/status.go:161 +0x29f
github.com/pingcap/dm/dm/worker.(*Worker).QueryError(0xc00012a000, 0xc002c95250, 0x9, 0x0, 0x0, 0x0)
	/home/jenkins/agent/workspace/build_dm_master/go/src/github.com/pingcap/dm/dm/worker/worker.go:348 +0x110
github.com/pingcap/dm/dm/worker.(*Server).QueryError(0xc000500080, 0x206eb60, 0xc0008ea150, 0xc0049ff470, 0xc000500080, 0xc0008ea150, 0xc000285a80)
	/home/jenkins/agent/workspace/build_dm_master/go/src/github.com/pingcap/dm/dm/worker/server.go:284 +0x2b9
github.com/pingcap/dm/dm/pb._Worker_QueryError_Handler(0x1c75ca0, 0xc000500080, 0x206eb60, 0xc0008ea150, 0xc00365a540, 0x0, 0x206eb60, 0xc0008ea150, 0xc002c95240, 0xb)
	/home/jenkins/agent/workspace/build_dm_master/go/src/github.com/pingcap/dm/dm/pb/dmworker.pb.go:3811 +0x217
google.golang.org/grpc.(*Server).processUnaryRPC(0xc00048f800, 0x208c180, 0xc0001b0600, 0xc005fa4e00, 0xc000442f60, 0x33b1fc0, 0x0, 0x0, 0x0)
	/go/pkg/mod/google.golang.org/grpc@v1.25.1/server.go:1007 +0x460
google.golang.org/grpc.(*Server).handleStream(0xc00048f800, 0x208c180, 0xc0001b0600, 0xc005fa4e00, 0x0)
	/go/pkg/mod/google.golang.org/grpc@v1.25.1/server.go:1287 +0xd97
google.golang.org/grpc.(*Server).serveStreams.func1.1(0xc0000501d0, 0xc00048f800, 0x208c180, 0xc0001b0600, 0xc005fa4e00)
	/go/pkg/mod/google.golang.org/grpc@v1.25.1/server.go:722 +0xbb
created by google.golang.org/grpc.(*Server).serveStreams.func1
	/go/pkg/mod/google.golang.org/grpc@v1.25.1/server.go:720 +0xa1

4. Versions of the cluster

   • DM version (run dmctl -V or dm-worker -V or dm-master -V):

     DM v1.0.3