Define JSON_INVALID_UTF8_SUBSTITUTE PHP < 7.2

If PHP version is < 7.2 JSON_INVALID_UTF8_SUBSTITUTE is not defined.

In such case it can be defined to 0 so that it does not have any effect but the code can still be executed without crashing

src/Elasticsearch/Serializers/ArrayToJSONSerializer.php

@@ -6,6 +6,11 @@
 
 use Elasticsearch\Common\Exceptions\RuntimeException;
 
+if (!defined('JSON_INVALID_UTF8_SUBSTITUTE')) {
+    //PHP < 7.2 Define it as 0 so it does nothing
+    define('JSON_INVALID_UTF8_SUBSTITUTE', 0);
+}
+
 /**
  * Class JSONSerializer
  *

src/Elasticsearch/Serializers/EverythingToJSONSerializer.php

@@ -6,6 +6,11 @@
 
 use Elasticsearch\Common\Exceptions\RuntimeException;
 
+if (!defined('JSON_INVALID_UTF8_SUBSTITUTE')) {
+    //PHP < 7.2 Define it as 0 so it does nothing
+    define('JSON_INVALID_UTF8_SUBSTITUTE', 0);
+}
+
 /**
  * Class EverythingToJSONSerializer
  *

src/Elasticsearch/Serializers/SmartSerializer.php

@@ -7,6 +7,11 @@
 use Elasticsearch\Common\Exceptions;
 use Elasticsearch\Common\Exceptions\Serializer\JsonErrorException;
 
+if (!defined('JSON_INVALID_UTF8_SUBSTITUTE')) {
+    //PHP < 7.2 Define it as 0 so it does nothing
+    define('JSON_INVALID_UTF8_SUBSTITUTE', 0);
+}
+
 /**
  * Class SmartSerializer
  *