[XDCR] panic: runtime error: invalid memory address or nil pointer dereference

Observed in 7.0.0-2954

Test passed in next build 7.0.0-2956

From xdcr log (.153):

2020-08-27T03:40:34.638-07:00 INFO GOXDCR.XmemNozzle: xmem_6543fa1c737be2198568a5e14a291bda/default/default_172.23.107.184:11210_0 checking routine exits
2020-08-27T03:40:34.638-07:00 INFO GOXDCR.XmemNozzle: xmem_6543fa1c737be2198568a5e14a291bda/default/default_172.23.107.184:11210_0 selfMonitor routine exits
2020-08-27T03:40:34.639-07:00 INFO GOXDCR.DcpNozzle: dcp_6543fa1c737be2198568a5e14a291bda/default/default_172.23.105.153:11210_1: all dcp stream have been initialized.
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x2 pc=0x8d190d]

goroutine 473 [running]:
github.com/couchbase/goxdcr/parts.(*XmemNozzle).batchGetXattrForCustomCR(0xc00044a800, 0xc000c2cae0, 0x0, 0x1, 0x1, 0x0)
/home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/goxdcr/parts/xmem_nozzle.go:1972 +0x3ad
github.com/couchbase/goxdcr/parts.(*XmemNozzle).processData_sendbatch(0xc00044a800, 0xc000262620, 0xc00044aa4c, 0x0, 0x0)
/home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/goxdcr/parts/xmem_nozzle.go:1215 +0x77c
created by github.com/couchbase/goxdcr/parts.(*XmemNozzle).Start
/home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/goxdcr/parts/xmem_nozzle.go:994 +0x523
2020-08-27T03:40:34.759-07:00 INFO GOXDCR.ReplMgr: GOMAXPROCS=4
2020-08-27T03:40:34.762-07:00 INFO GOXDCR.AuditSvc: Created audit service.
2020-08-27T03:40:34.762-07:00 INFO GOXDCR.UILogSvc: Created ui log service.
2020-08-27T03:40:35.277-07:00 INFO GOXDCR.RemClusterSvc: Agent remoteCluster/VNSfrqTOZckPWPfBYB

Job: http://server.jenkins.couchbase.com/job/build_sanity_matrix/7950/DISTRO=centos7,TYPE=4node/