PHPC-1713: Ensure Cursor::current returns null on invalid positions (#1186)

* Ensure Cursor::current returns null on invalid positions

* Addressed code review feedback

Author: alcaeus

src/MongoDB/Cursor.c

@@ -311,7 +311,9 @@ PHP_METHOD(Cursor, current)
 
 	data = php_phongo_cursor_get_current_data(intern);
 
-	if (data) {
+	if (Z_ISUNDEF_P(data)) {
+		RETURN_NULL();
+	} else {
 		ZVAL_COPY_DEREF(return_value, data);
 	}
 }

tests/cursor/bug1713-001.phpt

@@ -0,0 +1,23 @@
+--TEST--
+PHPC-1713: MongoDB\Driver\Cursor::current() does not return anything
+--SKIPIF--
+<?php require __DIR__ . "/../utils/basic-skipif.inc"; ?>
+<?php skip_if_not_live(); ?>
+--FILE--
+<?php
+require_once __DIR__ . "/../utils/basic.inc";
+
+$manager = new MongoDB\Driver\Manager(URI);
+
+$cursor = $manager->executeQuery(NS, new MongoDB\Driver\Query([]));
+
+var_dump($cursor->valid());
+var_dump($cursor->current());
+
+?>
+===DONE===
+<?php exit(0); ?>
+--EXPECTF--
+bool(false)
+NULL
+===DONE===