Fix tmux startup oops regarding mouse mode initial setting.

tmux/.tmux.conf

@@ -77,7 +77,7 @@ bind-key s \
 # same thing as ^ so it sets up things if we were started with
 # something else that set synchronization.
 if-shell \
-  "tmux show-window-options | grep 'synchronize-panes on'" \
+  "tmux show-window-options | grep 'synchronize-panes on' || /bin/true" \
   "set-window-option window-status-current-bg red; \
   set-window-option pane-active-border-fg yellow; \
   set-window-option pane-active-border-bg red"