This was partly fixed by 475c341 (calcurse-caldav: Fix late retrieval of ETag, 2016-01-25). However, the case where the server does not return ETag after creating a new item still wasn't handled properly. This patch hopefully addresses this and also makes sure that the ETag header is matched case-insensitively. Signed-off-by: Lukas Fleischer <lfleischer@calcurse.org>