Prevent log_query to mess up regular execution flow

When the "log_query" debug config parameter is set, SQL queries are
logged. However, if an error occurs when converting the values to
string, it will abort the request.

This fix catches the error and continues instead.

Also added handler for DateTime value which is already known to cause
aborts here.

Signed-off-by: Vincent Petry <vincent@nextcloud.com>