Fixed nullpointer when receiving requested tx after pruned state confirmed

Author: Brord van Wierst

src/main/java/com/iota/iri/service/transactionpruning/impl/PrunedTransactionVerifierImpl.java

@@ -84,7 +84,7 @@ public boolean isPruned(Hash hash) throws PrunedTransactionException{
     public void submitTransaction(TransactionViewModel receivedTransactionViewModel) throws PrunedTransactionException {
         Hash parent = receivedTransactionViewModel.getHash();
         Hash child = getChildForParent(parent);
-        if (isPruned(child)) {
+        if (child == null || isPruned(child)) {
             // We succeeded in the meantime.
             return;
         }
@@ -95,7 +95,7 @@ public void submitTransaction(TransactionViewModel receivedTransactionViewModel)
 
             if (isPruned(child)) {
                 // We succeeded in the meantime.
-                clean(child);
+                parents.remove(child);
                 return;
             }