Fix bug when Multiple is passed an invalid value

If you are using `Multiple` to validate, and pass a value that is unsupported by the `%` operator, it will fail instead of creating a validation error. This fixes that bug.

library/Rules/Multiple.php

@@ -9,6 +9,10 @@
 
 namespace Respect\Validation\Rules;
 
+use function filter_var;
+
+use const FILTER_VALIDATE_INT;
+
 /**
  * @author Danilo Benevides <[email protected]>
  * @author Henrique Moody <[email protected]>
@@ -31,6 +35,9 @@ public function __construct(int $multipleOf)
      */
     public function validate($input): bool
     {
+        if (filter_var($input, FILTER_VALIDATE_INT) === false) {
+            return false;
+        }
         if ($this->multipleOf == 0) {
             return $input == 0;
         }