Fix division by zero

backend/src/main/kotlin/space/rethelyi/model/Machine.kt

@@ -29,13 +29,7 @@ enum class Kind {
 }
 
 val Machine.status: Status get() {
-    var averagePower = 0
-    power.forEach { p ->
-        averagePower += p
-    }
-    averagePower /= power.size
-
-    return if (averagePower > threshold) {
+    return if (power.average() > threshold) {
         Status.NotAvailable
     } else {
         Status.Available