premix: fixes debug tool, dispose db changes

premix/debug.nim

@@ -20,6 +20,7 @@ proc executeBlock(blockEnv: JsonNode, memoryDB: TrieDatabaseRef, blockNumber: Ui
     body   = chainDB.getBlockBody(header.blockHash)
 
   let
+    transaction = memoryDB.beginTransaction()
     vmState = newBaseVMState(parent, chainDB)
     validationResult = processBlock(chainDB, parent, header, body, vmState)
 
@@ -28,6 +29,9 @@ proc executeBlock(blockEnv: JsonNode, memoryDB: TrieDatabaseRef, blockNumber: Ui
   else:
     info "block validation success", validationResult, blockNumber
 
+  # success or not dispose it
+  transaction.dispose()
+  
   dumpDebuggingMetaData(chainDB, header, body, vmState, false)
   let
     fileName = "debug" & $blockNumber & ".json"