Restrict load-session command to within Tmux to avoid an odd bug

libexec/tmuxifier-load-session

@@ -13,4 +13,9 @@ fi
 # Load runtime functions.
 source "$TMUXIFIER/runtime.sh"
 
-load_session "$1"
+if [ ! -z $TMUX ]; then
+  load_session "$1"
+else
+  echo "tmuxifier: 'load-session' command can only be used from within Tmux."
+  exit 1
+fi