dbi: return small dirent buffer on Windows
dbi: return small dirent buffer on Windows

First, not only do we need to test for __MINGW32__, but the broader
_WIN32. Second, a return value of zero means that determining the
buffer size failed, which is not quite the case, so just return 1 for
now.

cention-nazri/libdbi,cention-nazri/libdbi,cention-nazri/libdbi