Fix map access panic (#343)

## Describe your changes and provide context
- `CollectIteratorItems` needs to hold an RLock to avoid a concurrent
access panic

## Testing performed to validate your change
- Reproduced through a sei-chain-side test (concurrent instantiates)

store/multiversion/store.go

@@ -206,7 +206,7 @@ func (s *Store) SetEstimatedWriteset(index int, incarnation int, writeset WriteS
 	s.txWritesetKeys[index] = writeSetKeys
 }
 
-// GetWritesetKeys implements MultiVersionStore.
+// GetAllWritesetKeys implements MultiVersionStore.
 func (s *Store) GetAllWritesetKeys() map[int][]string {
 	s.mtx.RLock()
 	defer s.mtx.RUnlock()
@@ -243,10 +243,13 @@ func (s *Store) GetIterateset(index int) Iterateset {
 
 // CollectIteratorItems implements MultiVersionStore. It will return a memDB containing all of the keys present in the multiversion store within the iteration range prior to (exclusive of) the index.
 func (s *Store) CollectIteratorItems(index int) *db.MemDB {
+	s.mtx.RLock()
+	defer s.mtx.RUnlock()
+
 	sortedItems := db.NewMemDB()
 
 	// get all writeset keys prior to index
-	keys := s.GetAllWritesetKeys()
+	keys := s.txWritesetKeys
 	for i := 0; i < index; i++ {
 		indexedWriteset, ok := keys[i]
 		if !ok {
@@ -316,21 +319,27 @@ func (s *Store) validateIterator(index int, tracker iterationTracker) bool {
 	}
 }
 
-// TODO: do we want to return bool + []int where bool indicates whether it was valid and then []int indicates only ones for which we need to wait due to estimates? - yes i think so?
-func (s *Store) ValidateTransactionState(index int) (bool, []int) {
-	defer telemetry.MeasureSince(time.Now(), "store", "mvs", "validate")
-	conflictSet := map[int]struct{}{}
-	valid := true
+func (s *Store) checkIteratorAtIndex(index int) bool {
+	s.mtx.RLock()
+	defer s.mtx.RUnlock()
 
-	// TODO: can we parallelize for all iterators?
-	iterateset := s.GetIterateset(index)
+	valid := true
+	iterateset := s.txIterateSets[index]
 	for _, iterationTracker := range iterateset {
 		iteratorValid := s.validateIterator(index, iterationTracker)
 		valid = valid && iteratorValid
 	}
+	return valid
+}
+
+func (s *Store) checkReadsetAtIndex(index int) (bool, []int) {
+	s.mtx.RLock()
+	defer s.mtx.RUnlock()
+
+	conflictSet := make(map[int]struct{})
+	readset := s.txReadSets[index]
+	valid := true
 
-	// validate readset
-	readset := s.GetReadset(index)
 	// iterate over readset and check if the value is the same as the latest value relateive to txIndex in the multiversion store
 	for key, value := range readset {
 		// get the latest value from the multiversion store
@@ -357,16 +366,28 @@ func (s *Store) ValidateTransactionState(index int) (bool, []int) {
 		}
 	}
 
-	// convert conflictset into sorted indices
 	conflictIndices := make([]int, 0, len(conflictSet))
 	for index := range conflictSet {
 		conflictIndices = append(conflictIndices, index)
 	}
 
 	sort.Ints(conflictIndices)
+
 	return valid, conflictIndices
 }
 
+// TODO: do we want to return bool + []int where bool indicates whether it was valid and then []int indicates only ones for which we need to wait due to estimates? - yes i think so?
+func (s *Store) ValidateTransactionState(index int) (bool, []int) {
+	defer telemetry.MeasureSince(time.Now(), "store", "mvs", "validate")
+
+	// TODO: can we parallelize for all iterators?
+	iteratorValid := s.checkIteratorAtIndex(index)
+
+	readsetValid, conflictIndices := s.checkReadsetAtIndex(index)
+
+	return iteratorValid && readsetValid, conflictIndices
+}
+
 func (s *Store) WriteLatestToStore() {
 	s.mtx.Lock()
 	defer s.mtx.Unlock()