[CMake] file( DOWNLOAD ) problem

[Robert Dailey]

I'm using the file( DOWNLOAD ) command to download some files from an
FTP server. I notice that if I  put a completely invalid URL to a
file, the destination file is still created in Windows with a size of
0 bytes. This tricks my logic into thinking the download was
successful (since I only check if the destination file exists). Is
this a bug or a feature? If it's a feature, what is a reliable way I
can determine if the download succeeded?