Build fails on 32bit architectures

```cpp
../src/wutil.cpp: In function 'int fd_check_is_remote(int)':
../src/wutil.cpp:311:14: error: narrowing conversion of '4283649346' from 'unsigned int' to 'int' [-Wnarrowing]
  311 |         case 0xFF534D42:  // CIFS_MAGIC_NUMBER
      |              ^~~~~~~~~~
```