Fixed NPE introduced in earlier commit.

src/main/java/org/qortal/controller/Controller.java

@@ -1421,11 +1421,13 @@ public class Controller extends Thread {
 
 				BlockData blockData = repository.getBlockRepository().fromReference(parentSignature);
 
+				if (blockData != null) {
 					if (PruneManager.getInstance().isBlockPruned(blockData.getHeight(), repository)) {
 						// If this request contains a pruned block, we likely only have partial data, so best not to sent anything
 						// We always prune from the oldest first, so it's fine to just check the first block requested
 						blockData = null;
 					}
+				}
 
 				while (blockData != null && blockSummaries.size() < numberRequested) {
 					BlockSummaryData blockSummary = new BlockSummaryData(blockData);