Set UNION bit for internal class union return type

Fixes assertion failure reported in:
php#7115 (comment)

Author: nikic

Zend/zend_API.c

@@ -2806,6 +2806,7 @@ ZEND_API zend_result zend_register_functions(zend_class_entry *scope, const zend
 						zend_type_list *list = malloc(ZEND_TYPE_LIST_SIZE(num_types));
 						list->num_types = num_types;
 						ZEND_TYPE_SET_LIST(new_arg_info[i].type, list);
+						ZEND_TYPE_FULL_MASK(new_arg_info[i].type) |= _ZEND_TYPE_UNION_BIT;
 
 						const char *start = class_name;
 						uint32_t j = 0;

ext/reflection/tests/ReflectionMethod_tentative_return_type.phpt

@@ -12,29 +12,24 @@ class MyDateTimeZone extends DateTimeZone
     }
 }
 
-$methodInfo = new ReflectionMethod(DateTimeZone::class, 'listIdentifiers');
-
-var_dump($methodInfo->hasReturnType());
-var_dump($methodInfo->hasTentativeReturnType());
-var_dump($methodInfo->getReturnType());
-var_dump((string) $methodInfo->getTentativeReturnType());
-var_dump((string) $methodInfo);
-echo "\n";
-
-$methodInfo = new ReflectionMethod(MyDateTimeZone::class, 'listIdentifiers');
+function printInfo(ReflectionMethod $methodInfo) {
+    var_dump($methodInfo->hasReturnType());
+    var_dump($methodInfo->hasTentativeReturnType());
+    var_dump((string) $methodInfo->getReturnType());
+    var_dump((string) $methodInfo->getTentativeReturnType());
+    var_dump((string) $methodInfo);
+    echo "\n";
+}
 
-var_dump($methodInfo->hasReturnType());
-var_dump($methodInfo->hasTentativeReturnType());
-var_dump((string) $methodInfo->getReturnType());
-var_dump($methodInfo->getTentativeReturnType());
-var_dump((string) $methodInfo);
-echo "\n";
+printInfo(new ReflectionMethod(DateTimeZone::class, 'listIdentifiers'));
+printInfo(new ReflectionMethod(MyDateTimeZone::class, 'listIdentifiers'));
+printInfo(new ReflectionMethod(FileSystemIterator::class, 'current'));
 
 ?>
 --EXPECTF--
 bool(false)
 bool(true)
-NULL
+string(0) ""
 string(5) "array"
 string(%d) "Method [ <internal:date> static public method listIdentifiers ] {
 
@@ -49,7 +44,7 @@ string(%d) "Method [ <internal:date> static public method listIdentifiers ] {
 bool(true)
 bool(false)
 string(6) "string"
-NULL
+string(0) ""
 string(%d) "Method [ <user, overwrites DateTimeZone, prototype DateTimeZone> static public method listIdentifiers ] {
   @@ %s
 
@@ -60,3 +55,15 @@ string(%d) "Method [ <user, overwrites DateTimeZone, prototype DateTimeZone> sta
   - Return [ string ]
 }
 "
+
+bool(false)
+bool(true)
+string(0) ""
+string(37) "SplFileInfo|FilesystemIterator|string"
+string(191) "Method [ <internal:SPL, overwrites DirectoryIterator, prototype Iterator> public method current ] {
+
+  - Parameters [0] {
+  }
+  - Tentative return [ SplFileInfo|FilesystemIterator|string ]
+}
+"