zsh:zprofile: Attach to tmux only when it exists

.config/zsh/.zprofile

@@ -104,7 +104,9 @@ if command -v startx &>/dev/null && [[ -z $DISPLAY && $XDG_VTNR -eq 1 ]]; then
 fi
 
 # Attach to tmux session if connected over ssh and not already attached
-if [[ (-n $SSH_CLIENT || -n $SSH_TTY || -n $SSH_CONNECTION) && -z $TMUX ]]; then
+if (( $+commands[tmux] )) &&
+	[[ (-n $SSH_CLIENT || -n $SSH_TTY || -n $SSH_CONNECTION) && -z $TMUX ]]
+then
 	num_sessions="$(tmux list-sessions 2>/dev/null | wc -l)"
 
 	if (( ! num_sessions )); then