Silent warning from is_readable

They emit warning in open_basedir mode.

Signed-off-by: Michal Čihař <michal@cihar.com>
Detect failure of curl_init

Signed-off-by: Michal Čihař <michal@cihar.com>
Check if set before using

Signed-off-by: Michal Čihař <michal@cihar.com>