Don't hard fail on sparse setup error

It seems this can fail in some casees, but proceed
with the download anyway.

server/sparse_windows.go

@@ -6,8 +6,9 @@ import (
 	"golang.org/x/sys/windows"
 )
 
-func setSparse(file *os.File) error {
-	return windows.DeviceIoControl(
+func setSparse(file *os.File) {
+	// exFat (and other FS types) don't support sparse files, so ignore errors
+	windows.DeviceIoControl( //nolint:errcheck
 		windows.Handle(file.Fd()), windows.FSCTL_SET_SPARSE,
 		nil, 0,
 		nil, 0,