Fix race condition and defensive checks for spam-clicking

Author: gourijain026@gmail.com

js/activity.js

@@ -1655,7 +1655,7 @@ class Activity {
 
         this._doFastButton = env => {
             // Prevent spam-clicking by checking if already running
-            if (this.logo._alreadyRunning) {
+            if (this.logo._alreadyRunning || this._restartPending) {
                 return;
             }
 
@@ -1691,11 +1691,17 @@ class Activity {
                     this.logo.step();
                 } else {
                     // Stop and restart.
+                    if (this._restartPending) {
+                        return;
+                    }
+
                     document.getElementById("stop").style.color = "white";
                     this.logo.doStopTurtles();
 
+                    this._restartPending = true;
                     const that = this;
                     setTimeout(() => {
+                        this._restartPending = false;
                         document.getElementById("stop").style.color = "#ea174c";
                         that.logo.runLogoCommands(null, env);
                     }, 500);

js/logo.js

@@ -1098,6 +1098,7 @@ class Logo {
      */
     runLogoCommands(startHere, env) {
         this._prematureRestart = this._alreadyRunning;
+        this._alreadyRunning = true;
         if (this._alreadyRunning && this._runningBlock !== null) {
             this._ignoringBlock = this._runningBlock;
         } else {
@@ -1404,8 +1405,6 @@ class Logo {
      * @returns {void}
      */
     runFromBlockNow(logo, turtle, blk, isflow, receivedArg, queueStart) {
-        this._alreadyRunning = true;
-
         this.receivedArg = receivedArg;
 
         // Sometimes we don't want to unwind the entire queue.
@@ -1760,7 +1759,7 @@ class Logo {
             if (!logo._prematureRestart) {
                 // Make sure any unissued signals are dispatched.
                 for (const b in tur.endOfClampSignals) {
-                    const signalsLength = tur.endOfClampSignals[b].length;
+                    const signalsLength = (tur.endOfClampSignals[b] && tur.endOfClampSignals[b].length) || 0;
                     for (let i = 0; i < signalsLength; i++) {
                         if (tur.endOfClampSignals[b][i] != null) {
                             if (