Fixed issue with throwing exception on undefined offset.

Author: Sevavietl

src/BaseArray.php

@@ -54,7 +54,7 @@ public function offsetGet($offset) {
             return $this->container[$offset];
         }
 
-        return $this->undefinedOffsetAction($this->container, $offset);
+        return ($this->undefinedOffsetAction)($this->container, $offset);
     }
 
     public function offsetSet($offset, $value) {

tests/unit/BaseArrayTest.php

@@ -3,6 +3,7 @@
 namespace Sevavietl\Arrays\Tests\Unit;
 
 use Sevavietl\Arrays\BaseArray;
+use Sevavietl\Arrays\UndefinedOffsetException;
 
 class BaseArrayTest extends \TestCase
 {
@@ -40,4 +41,12 @@ public function instantiationThrowsExceptionDataProvider()
             [new \StdClass],
         ];
     }
+
+    public function testThrowsExceptionOnUndefinedOffset()
+    {
+        $this->expectException(UndefinedOffsetException::class);
+
+        $arr = new BaseArray([1, 2, 3]);
+        $arr[3];
+    }
 }