Constant deltachat::download::MIN_DOWNLOAD_LIMIT

pub(crate) const MIN_DOWNLOAD_LIMIT: u32 = 163840;

Download limits should not be used below MIN_DOWNLOAD_LIMIT.

For better UX, some messages as add-member, non-delivery-reports (NDN) or read-receipts (MDN) should always be downloaded completely to handle them correctly, also in larger groups and if group and contact avatar are attached. Most of these cases are caught by MIN_DOWNLOAD_LIMIT.