Handle the case where our block headers are synced already (#2021)

chain-test/src/test/scala/org/bitcoins/chain/blockchain/ChainHandlerTest.scala

@@ -392,6 +392,20 @@ class ChainHandlerTest extends ChainDbUnitTest {
 
   }
 
+  it must "return None for ChainHandler.nextBlockHeaderBatchRange if we are synced" in {
+    chainHandler: ChainHandler =>
+      val genesisHeader =
+        chainHandler.chainConfig.chain.genesisBlock.blockHeader
+      val assert1F = for {
+        rangeOpt <-
+          chainHandler.nextBlockHeaderBatchRange(genesisHeader.hashBE, 1)
+        count <- chainHandler.getBlockCount()
+      } yield {
+        assert(rangeOpt.isEmpty)
+      }
+      assert1F
+  }
+
   it must "generate a range for a block filter header query" in {
     chainHandler: ChainHandler =>
       for {

chain/src/main/scala/org/bitcoins/chain/blockchain/ChainHandler.scala

@@ -199,9 +199,22 @@ case class ChainHandler(
 
     for {
       chains <- chainsF
-    } yield getBestChainAtHeight(startHeight = startHeight,
-                                 batchSize = batchSize,
-                                 blockchains = chains)
+    } yield {
+      val nextBlockHeaderOpt = getBestChainAtHeight(startHeight = startHeight,
+                                                    batchSize = batchSize,
+                                                    blockchains = chains)
+      (nextBlockHeaderOpt, prevBlockHeaderOpt) match {
+        case (Some(next), Some(prev)) =>
+          //this means we are synced, so return None
+          if (next.stopBlockHash == prev.hash) {
+            None
+          } else {
+            nextBlockHeaderOpt
+          }
+        case (Some(_), None) | (None, Some(_)) | (None, None) =>
+          nextBlockHeaderOpt
+      }
+    }
   }
 
   /** Given a vector of blockchains, this method finds the chain with the most chain work