Fix for segfault in Database::CheckStatus() when using MariaDB.

MariaDB returns NULL instead of 0 when an argument is passed that is out of range
(https://mariadb.com/kb/en/unix_timestamp/)


When the column 'suspendeduntil' of an entry in the 'account' table is out of range (e.g., the default value '0000-00-00 00:00:00'), undefined behavior results in Database::CheckStatus() from common/database.cpp since it essentially calls atoi(NULL), which generally causes a segfault.


On another note, isn't there a safer alternative to atoi() that can be used?