Merge bitcoin/bitcoin#26409: refactor: Silence GCC Wmissing-field-initializers in ChainstateManagerOpts

fa29ef0 refactor: Silence GCC Wmissing-field-initializers in ChainstateManagerOpts (MacroFake)

Pull request description:

  The `std::optional` fields in the struct that fall back to chain param defaults if not provided should be initialized to `std::nullopt`. This already happens with the current code.

  However, for consistency with `check_block_index` and to silence a GCC warning, add the "missing" `{}`.

ACKs for top commit:
  achow101:
    ACK fa29ef0
  hebasto:
    ACK fa29ef0, tested on Ubuntu 22.04 + GCC 11.3.
  jonatack:
    ACK fa29ef0

Tree-SHA512: bdec9c56df5d601a5616e107fed48737b13b0a7242b6526092fb682b5016544a4bc08666b60304c668d44c6f7ac69d3788093d921382c1d6c577c1f9fe31fc50

Author: achow101

src/kernel/chainstatemanager_opts.h

@@ -31,9 +31,9 @@ struct ChainstateManagerOpts {
     std::optional<bool> check_block_index{};
     bool checkpoints_enabled{DEFAULT_CHECKPOINTS_ENABLED};
     //! If set, it will override the minimum work we will assume exists on some valid chain.
-    std::optional<arith_uint256> minimum_chain_work;
+    std::optional<arith_uint256> minimum_chain_work{};
     //! If set, it will override the block hash whose ancestors we will assume to have valid scripts without checking them.
-    std::optional<uint256> assumed_valid_block;
+    std::optional<uint256> assumed_valid_block{};
     //! If the tip is older than this, the node is considered to be in initial block download.
     std::chrono::seconds max_tip_age{DEFAULT_MAX_TIP_AGE};
 };