rpc: reduce LOCK(cs_main) scope in blockToJSON

Author: andrewtoth

src/rpc/blockchain.cpp

@@ -181,7 +181,8 @@ UniValue blockToJSON(BlockManager& blockman, const CBlock& block, const CBlockIn
         case TxVerbosity::SHOW_DETAILS:
         case TxVerbosity::SHOW_DETAILS_AND_PREVOUT:
             CBlockUndo blockUndo;
-            const bool have_undo{WITH_LOCK(::cs_main, return !blockman.IsBlockPruned(blockindex) && UndoReadFromDisk(blockUndo, blockindex))};
+            const bool is_not_pruned{WITH_LOCK(::cs_main, return !blockman.IsBlockPruned(blockindex))};
+            const bool have_undo{is_not_pruned && UndoReadFromDisk(blockUndo, blockindex)};
 
             for (size_t i = 0; i < block.vtx.size(); ++i) {
                 const CTransactionRef& tx = block.vtx.at(i);