Merge bitcoin/bitcoin#26090: fs: fully initialize _OVERLAPPED for win32

02c9e56 fs: fully initialize _OVERLAPPED for win32 (Cory Fields)

Pull request description:

  ```bash
  fs.cpp: In member function ‘bool fsbridge::FileLock::TryLock()’:
  fs.cpp:129:32: error: missing initializer for member ‘_OVERLAPPED::InternalHigh’ [-Werror=missing-field-initializers]
    129 |     _OVERLAPPED overlapped = {0};
        |                                ^
  fs.cpp:129:32: error: missing initializer for member ‘_OVERLAPPED::<anonymous>’ [-Werror=missing-field-initializers]
  fs.cpp:129:32: error: missing initializer for member ‘_OVERLAPPED::hEvent’ [-Werror=missing-field-initializers]
  ```

  Came up in #25972. That PR is now rebased on this change.

  Closes: #26006

ACKs for top commit:
  sipsorcery:
    tACK 02c9e56.
  hebasto:
    ACK 02c9e56, tested on Linux x86_64:

Tree-SHA512: 6a0495c34bd952b2bb8c994a1450da7d3eee61225bb4ff0ce009c013f5e29dba94bb1c3ecef9989dc18c939909fdc8eba690a38f96da431ae9d64c23656de7d0

Author: fanquake

src/fs.cpp

@@ -126,7 +126,7 @@ bool FileLock::TryLock()
     if (hFile == INVALID_HANDLE_VALUE) {
         return false;
     }
-    _OVERLAPPED overlapped = {0};
+    _OVERLAPPED overlapped = {};
     if (!LockFileEx(hFile, LOCKFILE_EXCLUSIVE_LOCK | LOCKFILE_FAIL_IMMEDIATELY, 0, std::numeric_limits<DWORD>::max(), std::numeric_limits<DWORD>::max(), &overlapped)) {
         reason = GetErrorReason();
         return false;