don't allow broken execute tab

Author: MathMan05

src/webpage/executeTab/etab.ts

@@ -84,6 +84,9 @@ class Etab {
 			updateSpeed();
 		};
 	}
+	isReady() {
+		return !!this.sys;
+	}
 	stop() {
 		this.stopped = true;
 		this.changeButtonStates();

src/webpage/index.ts

@@ -366,7 +366,7 @@ editButton.onclick = () => {
 	editArea();
 };
 executeButton.onclick = () => {
-	executeArea();
+	if (system.isReady()) executeArea();
 };
 let system = new Etab();