[Backport MB-48754 to 7.0.5] panic: runtime error: integer divide by zero

Build: 7.1.0-1345
TestSuite: magma_5dgm_collections_gsi_delete_bsc_7.0_P0
Test: ./testrunner -i /tmp/testexec.24873.ini -p gsi_type=plasma,get-cbcollect-info=True,reset_services=True,java_sdk_client=True,GROUP=P0,dgm_run=True,active_resident_threshold=5,bucket_size=256,bucket_storage=magma,java_sdk_client=True,skip_log_scan=False,bucket_storage=couchstore -t gsi.collections_index_delete_bsc.CollectionsIndexDeleteBSC.test_index_creation_with_keyspace_delete,default_bucket=false,force_clean=true,defer_build=False,item_to_delete=collection,GROUP=P0,gsi_type=plasma,get-cbcollect-info=True,reset_services=True,java_sdk_client=True,dgm_run=True,active_resident_threshold=5,bucket_size=256,bucket_storage=couchstore,skip_log_scan=False

Test steps:

• Have one node cluster with kv, n1ql and index services
• Create a bucket with 256 MB RAM
• Create one scope and one collection in it.
• Load docs tills we have 5% kv dgm
• Create a GSI index
• Delete collection
• GSI index got deleted as expected but we see below panic in the logs

  2021-09-26T08:27:21.512-07:00 [Info] plasmaSlice::Close Closed Slice Id 0, IndexInstId 3846006233656657015, PartitionId 0, IndexDefnId 3484245274810424452.

  2021-09-26T08:27:21.513-07:00 [Info] test_bucket/idx/Mainstore#3846006233656657015:0 Plasma: Plasma.Close: Begin closing plasma instance

  panic: runtime error: integer divide by zero

  goroutine 15471 [running]:

  github.com/couchbase/indexing/secondary/indexer.(*plasmaSlice).Insert(0xc00527b080, 0xc00b063da0, 0x16, 0x18, 0xc00aff7c30, 0xa, 0x10, 0xc00b086d80, 0x0, 0x0)

  /home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/indexing/secondary/indexer/plasma_slice.go:598 +0x1aa

  github.com/couchbase/indexing/secondary/indexer.(*flusher).processUpsert(0xc00b162200, 0xc00b0887e0, 0xc00aff7c30, 0xa, 0x10, 0xc00b086d80)

  /home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/indexing/secondary/indexer/flusher.go:508 +0x27a

  github.com/couchbase/indexing/secondary/indexer.(*flusher).flush(0xc00b162200, 0xc00b086d40, 0x3)

  /home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/indexing/secondary/indexer/flusher.go:460 +0x5a6

  github.com/couchbase/indexing/secondary/indexer.(*flusher).flushSingleMutation(0xc00b162200, 0xc00b086d40, 0x3)

  /home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/indexing/secondary/indexer/flusher.go:403 +0x4c

  github.com/couchbase/indexing/secondary/indexer.(*flusher).flushSingleVbucketUptoSeqno(0xc00b162200, 0x1532d08, 0xc0013faf00, 0xc00b000003, 0xc004be7b60, 0x2a, 0x9f, 0x171, 0x13cf901, 0xc00b2464e0, ...)

  /home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/indexing/secondary/indexer/flusher.go:327 +0x2a5

  created by github.com/couchbase/indexing/secondary/indexer.(*flusher).flushQueue

  /home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/indexing/secondary/indexer/flusher.go:198 +0x2a5

  Initializing write barrier = 8000

Logs: [^172.23.123.49-20210926-0828-diag.zip]