[tmux] M-o goes to previsous session if no last session

Since we only use two sessions most of the time, and I had to manully
navigate the first time opening tmux for it to register a "last session"
this makes a lot more sense.

Author: meain

tmux/.tmux.conf

@@ -91,7 +91,7 @@ bind-key -n M-w kill-pane
 bind-key -n M-u last-window
 
 # Easier session switching
-bind-key -n M-o switch-client -l
+bind-key -n M-o run-shell "tmux switch-client -l || tmux switch-client -p"
 
 # Kill tmux session
 bind 0 kill-session