Fix a bug where a JS script would never exit if killed in a sleep loop.

src/NetscriptFunctions.js

@@ -229,6 +229,7 @@ function NetscriptFunctions(workerScript) {
                 workerScript.scriptRef.log("Sleeping for " + time + " milliseconds");
             }
             return netscriptDelay(time, workerScript).then(function() {
+                if (workerScript.env.stopFlag) {return Promise.reject(workerScript);}
                 return Promise.resolve(true);
             });
         },