refactor: adding a check to isPrime()

Author: ROSSARKO

app/src/main/java/hexlet/code/games/Prime.java

@@ -6,6 +6,7 @@
 public class Prime {
     private static final int MIN = 2;
     private static final int MAX = 1000;
+
     public static void startGame() {
 
         String[][] roundsData = new String[Engine.ROUNDS][2];
@@ -21,6 +22,9 @@ public static void startGame() {
     }
 
     public static boolean isPrime(int num) {
+        if (num <= 0) {
+            return false;
+        }
         for (int i = 2; i <= Math.sqrt(num); i++) {
             if (num % i == 0) {
                 return false;