If a Windows program writes a registry key of type REG_DWORD but puts more than 4 bytes of data in—I can't imagine why, but I am working with such a program—currently it is persisted as-is in the `WINEPATH` but `regedit` exports it as a `dword:%08x`, truncating the data.
This patch makes sure that only 4-byte DWORDs are exported as `dword:`; any other size falls through as a `hex(4):`.
(I chose to use the literal `4` here instead of `sizeof(DWORD)` because this value isn't directly coupled to the size of a `DWORD` as the compiler sees it; in the (extremely hypothetical?) world in which Wine is compiled with a `DWORD` of some other size, this value should still be 4, because `export_dword_data` will only correctly export something that can be represented in 8 hexadecimal characters.)