Renumber windows: Lookup lastw via window not index
Renumber windows: Lookup lastw via window not index

When calling 'movew -r' on a session to reorder the winlinks, ensure
when adding back in the information for the lastw stack that we look up
the winlink based on the window and not its index.

Using the index doesn't make sense here because when comparing it to the
old set, it will never match since the winlink has been renumbered.

Bug reported by Ben Boeckel. Patch by Thomas Adam.

klaxalk/tmux,klaxalk/tmux,klaxalk/tmux,klaxalk/tmux,klaxalk/tmux