check if xset exists before executing it

zshrc.local

@@ -27,4 +27,6 @@ if which tmux 2>&1 >/dev/null; then
     test -z "$TMUX" && (tmux attach || tmux new-session)
 fi
 
-xset -b
+if which xset 2>&1 >/dev/null; then
+    xset -b
+fi