fix block size overflow

Author: sasaxie

src/main/java/org/tron/core/db/Manager.java

@@ -923,12 +923,10 @@ public synchronized BlockCapsule generateBlock(
       throw new IllegalArgumentException("generate block timestamp is invalid.");
     }
 
-    long currentTrxSize = 0;
     long postponedTrxCount = 0;
 
     final BlockCapsule blockCapsule =
         new BlockCapsule(number + 1, preHash, when, witnessCapsule.getAddress());
-    currentTrxSize = blockCapsule.getInstance().getSerializedSize();
     dialog.reset();
     dialog.setValue(revokingStore.buildDialog());
     Iterator iterator = pendingTransactions.iterator();
@@ -939,9 +937,8 @@ public synchronized BlockCapsule generateBlock(
         logger.debug("Processing transaction time exceeds the 50% producing time。");
         break;
       }
-      currentTrxSize += trx.getSerializedSize() + 2;
       // check the block size
-      if (currentTrxSize > ChainConstant.BLOCK_SIZE) {
+      if ((blockCapsule.getInstance().getSerializedSize() + trx.getSerializedSize() + 3) > ChainConstant.BLOCK_SIZE) {
         postponedTrxCount++;
         continue;
       }