File attributes are not set when their value is FALSE/NULL

Various file attributes are set only when their value is TRUE or NULL in the _g_local_file_info_get function (e.g. is-hidden, is-backup). They should be set in those cases as mentioned in !3261 (comment 1660703). This is another follow-up of !3261 (merged) that currently breaks the Nautilus pipeline among others. The g_file_info_has_attribute checks can be added in Nautilus, but I suppose that the standard attributes like the is-hidden/is-backup ones should be ideally guaranteed to be set...

Edit: The is-hidden attribute is not always set only in the case of G_OS_WIN32.