Add sanity check

crawler_software/arduino/crawler_slave/crawler_slave.ino

@@ -33,12 +33,14 @@ void loop() {
 
 // This method runs when we receive a message
 void receiveEvent(int n) {
-  id  = Wire.read(); // ID of the servo/device to access
-  val = Wire.read(); // Value to assign
-
-  switch(id) {
-    case 1:
-      windowWiperServo.write(val);
-      break;
+  if (Wire.available() == 2) { // Dont do anything if this is not true
+    id  = Wire.read(); // ID of the servo/device to access
+    val = Wire.read(); // Value to assign
+  
+    switch(id) {
+      case 1:
+        windowWiperServo.write(val);
+        break;
+    }
   }
 }