BUG: No prompt for session auto-load when unloaded buffers exist.

When file marks (e.g. 'A) cause unloaded buffers to exist on startup, the question for session auto-load isn't brought up.

bufnr('$') == 1 isn't a correct check; one needs to go through all existing buffers and check for listed ones that aren't the current one.
Merge branches 'drop-args-filtering', 'turn-off-menu', 'fix-tab-win-restore-order', 'handle-zero-height-windows' and 'fix-empty-buffer-list-check'