msi: Download the MSI package if it is a remote URL [try3]

[Dan Kegel]

James wrote:

+    GetUrlCacheEntryInfoW( szUrl, NULL, &size );
+    if ( GetLastError() != ERROR_FILE_NOT_FOUND )

Is it really ok to check GetLastError() to see if there's been an error?
I thought successful operations did not affect the value of GetLastError().

Something like

int succeeded = GetUrlCacheEntryInfoW( szUrl, NULL, &size );
if (succeeded)

seems cleaner to me.

- Dan