Fixed confused exception message while user threw exception

Zend/tests/bug64354.phpt

@@ -0,0 +1,24 @@
+--TEST--
+Bug #64354 (Unserialize array of objects whose class can't be autoloaded fail)
+--FILE--
+<?php
+class B implements Serializable {
+    public function serialize() {
+        throw new Exception("serialize");
+        return NULL;
+    }
+
+    public function unserialize($data) {
+    }
+}
+
+$data = array(new B);
+
+try {
+    serialize($data);
+} catch (Exception $e) { 
+    var_dump($e->getMessage());
+}
+?>
+--EXPECTF--
+string(9) "serialize"

Zend/zend_interfaces.c

@@ -452,7 +452,7 @@ ZEND_API int zend_user_serialize(zval *object, unsigned char **buffer, zend_uint
 		zval_ptr_dtor(&retval);
 	}
 
-	if (result == FAILURE) {
+	if (result == FAILURE && !EG(exception)) {
 		zend_throw_exception_ex(NULL, 0 TSRMLS_CC, "%s::serialize() must return a string or NULL", ce->name);
 	}
 	return result;