fix: do not rebuild an app that has never been deployed

plugins/ps/subcommands/rebuild

@@ -6,8 +6,14 @@ source "$PLUGIN_AVAILABLE_PATH/ps/functions"
 ps_rebuild_cmd() {
   declare desc="rebuilds an app from source"
   local cmd="ps:rebuild"
-  [[ -z $2 ]] && dokku_log_fail "Please specify an app to run the command on"
-  ps_rebuild "$2"
+  local APP="$2"
+  [[ -z "$APP" ]] && dokku_log_fail "Please specify an app to run the command on"
+
+  if (is_deployed "$APP"); then
+    ps_rebuild "$APP"
+  else
+    dokku_log_warn "App $APP has not been deployed"
+  fi
 }
 
 ps_rebuild_cmd "$@"