decompress crash seen in Plasma-GSI test

goroutine 140 [running]:
github.com/couchbase/plasma.(*Shard).raisePanic(...)
/data/jenkins/workspace/centos-2i_plasma_API_tests/cheshire-cat/goproj/src/github.com/couchbase/plasma/shard.go:1050
github.com/couchbase/plasma.(*LSSCtx).raiseCorrupted(0xc0002d8a00, 0xd58ba0, 0xc001f87610)
/data/jenkins/workspace/centos-2i_plasma_API_tests/cheshire-cat/goproj/src/github.com/couchbase/plasma/lssctx.go:185 +0x206
github.com/couchbase/plasma.(*Plasma).fatalPanic(0xc0000d4700, 0xc5e7b4, 0x11)
/data/jenkins/workspace/centos-2i_plasma_API_tests/cheshire-cat/goproj/src/github.com/couchbase/plasma/plasma.go:1523 +0x293
github.com/couchbase/plasma.(*page).checkMutable(0xc003b88040)
/data/jenkins/workspace/centos-2i_plasma_API_tests/cheshire-cat/goproj/src/github.com/couchbase/plasma/page.go:941 +0x68
github.com/couchbase/plasma.(*page).Decompress(0xc003b88040, 0x7f173002a800)
/data/jenkins/workspace/centos-2i_plasma_API_tests/cheshire-cat/goproj/src/github.com/couchbase/plasma/page.go:2044 +0x2f
github.com/couchbase/plasma.(*pageWalker).Decompress(0xc0036655f8, 0xc003b88040, 0xc003665650)
/data/jenkins/workspace/centos-2i_plasma_API_tests/cheshire-cat/goproj/src/github.com/couchbase/plasma/page_walker.go:337 +0x1b2
github.com/couchbase/plasma.(*Plasma).tryPageSwapin(0xc0000d4700, 0xd8c660, 0xc003b88040, 0xc003665600)
/data/jenkins/workspace/centos-2i_plasma_API_tests/cheshire-cat/goproj/src/github.com/couchbase/plasma/plasma.go:1581 +0x1e3
github.com/couchbase/plasma.(*Plasma).ReadPage(0xc0000d4700, 0x7f177effd3c0, 0xc8e201, 0xc001fa8240, 0xc000196eb8, 0x7f177effd3c0, 0x7f177effaff0, 0xc003088101)
/data/jenkins/workspace/centos-2i_plasma_API_tests/cheshire-cat/goproj/src/github.com/couchbase/plasma/pagetable.go:202 +0xf5
github.com/couchbase/plasma.(*Plasma).tryPageRemoval(0xc0000d4700, 0x7f177effaff0, 0xd8c660, 0xc001f6ddc0, 0xc001fa8240)
/data/jenkins/workspace/centos-2i_plasma_API_tests/cheshire-cat/goproj/src/github.com/couchbase/plasma/plasma.go:1129 +0x103
github.com/couchbase/plasma.(*Plasma).doPageMerge(0xc0000d4700, 0x7f177effaff0, 0xd8c660, 0xc001f6ddc0, 0xc001fa8240, 0x1)
/data/jenkins/workspace/centos-2i_plasma_API_tests/cheshire-cat/goproj/src/github.com/couchbase/plasma/plasma.go:1395 +0xeb
github.com/couchbase/plasma.(*Plasma).trySMOs2(0xc0000d4700, 0x7f177effaff0, 0xd8c660, 0xc001f6ddc0, 0xc001fa8240, 0xc001f6dd00, 0x190, 0x19, 0xc8, 0x4, ...)
/data/jenkins/workspace/centos-2i_plasma_API_tests/cheshire-cat/goproj/src/github.com/couchbase/plasma/plasma.go:1378 +0x1430
github.com/couchbase/plasma.(*Plasma).trySMOs(...)
/data/jenkins/workspace/centos-2i_plasma_API_tests/cheshire-cat/goproj/src/github.com/couchbase/plasma/plasma.go:1256
github.com/couchbase/plasma.(*Writer).Lookup(0xc001725280, 0x7f1733c53400, 0x1000, 0x1ffb, 0x0)
/data/jenkins/workspace/centos-2i_plasma_API_tests/cheshire-cat/goproj/src/github.com/couchbase/plasma/writer.go:158 +0x197
github.com/couchbase/plasma.(*Writer).LookupKV(0xc001725280, 0xc003b82000, 0x1000, 0x1ffb, 0x1000, 0x1000, 0x6, 0x716, 0x0)
/data/jenkins/workspace/centos-2i_plasma_API_tests/cheshire-cat/goproj/src/github.com/couchbase/plasma/mvcc.go:490 +0x10c
main.(*WorkerCtx).doRead(0xc001227a40)
/data/jenkins/workspace/centos-2i_plasma_API_tests/cheshire-cat/goproj/src/github.com/couchbase/plasma/tools/gsi/worker.go:204 +0x212
main.(*WorkerCtx).Run(0xc001227a40, 0x0)
/data/jenkins/workspace/centos-2i_plasma_API_tests/cheshire-cat/goproj/src/github.com/couchbase/plasma/tools/gsi/worker.go:310 +0x8d2
created by main.(*InstanceCtx).StartWorkers
/data/jenkins/workspace/centos-2i_plasma_API_tests/cheshire-cat/goproj/src/github.com/couchbase/plasma/tools/gsi/instance.go:209 +0x81
+ grep -Ei panic /data/jenkins/workspace/centos-2i_plasma_API_tests/cheshire-cat/goproj/src/github.com/couchbase/plasma/tools/gsi/output.txt
panic: : fatal: Page is immutable
github.com/couchbase/plasma.(*Shard).raisePanic(...)
github.com/couchbase/plasma.(*Plasma).fatalPanic(0xc0000d4700, 0xc5e7b4, 0x11)