[3.0.1 Backport] Compaction w/ import and xattrs enabled can panic

func TestImportCompactPanic(t *testing.T) {

	if !base.TestUseXattrs() {

		t.Skip("requires xattrs")

	}

	// Set the compaction and metadata purge interval unrealistically low to reproduce faster

	options := DatabaseContextOptions{

		CompactInterval: 1,

	}

	AddOptionsFromEnvironmentVariables(&options)

	bucket := base.GetTestBucket(t)

	dbc, err := NewDatabaseContext("db", bucket, true, options)

	require.NoError(t, err, "Couldn't create context for database 'db'")

	dbc.PurgeInterval = time.Millisecond

	db, err := CreateDatabase(dbc)

	require.NoError(t, err, "Couldn't create database 'db'")

	// Create a document, then delete it

	rev, doc, err := db.Put("test", Body{})

	require.NoError(t, err)

	_, err = db.DeleteDoc(doc.ID, rev)

	require.NoError(t, err)

	waitForBGTCompletion(BGTCompletionMaxWait, db.backgroundTasks, db.Name)

}

2022/05/04 15:41:11 Unexpected panic: runtime error: invalid memory address or nil pointer dereference - stopping process

goroutine 1750 [running]:

runtime/debug.Stack()

	/Users/marks.polakovs@couchbase.com/sdk/go1.17.9/src/runtime/debug/stack.go:24 +0x65

github.com/couchbase/sync_gateway/base.FatalPanicHandler()

	/Users/marks.polakovs@couchbase.com/code/sync_gateway_3.0.1/godeps/src/github.com/couchbase/sync_gateway/base/util.go:1476 +0x49

panic({0x1b2ef60, 0x26cfc90})

	/Users/marks.polakovs@couchbase.com/sdk/go1.17.9/src/runtime/panic.go:1038 +0x215

github.com/couchbase/sync_gateway/base.(*SafeTerminator).Done(...)

	/Users/marks.polakovs@couchbase.com/code/sync_gateway_3.0.1/godeps/src/github.com/couchbase/sync_gateway/base/util.go:1280

github.com/couchbase/sync_gateway/db.(*Database).Compact(0xc002c903c0, 0x0, 0x1d62450, 0x0)

	/Users/marks.polakovs@couchbase.com/code/sync_gateway_3.0.1/godeps/src/github.com/couchbase/sync_gateway/db/database.go:1163 +0x783

github.com/couchbase/sync_gateway/db.NewDatabaseContext.func10({0x1eaf300, 0xc002c90c30})

	/Users/marks.polakovs@couchbase.com/code/sync_gateway_3.0.1/godeps/src/github.com/couchbase/sync_gateway/db/database.go:548 +0x85

github.com/couchbase/sync_gateway/db.NewBackgroundTask.func1()

	/Users/marks.polakovs@couchbase.com/code/sync_gateway_3.0.1/godeps/src/github.com/couchbase/sync_gateway/db/utils.go:46 +0x237

created by github.com/couchbase/sync_gateway/db.NewBackgroundTask

	/Users/marks.polakovs@couchbase.com/code/sync_gateway_3.0.1/godeps/src/github.com/couchbase/sync_gateway/db/utils.go:37 +0x331