Fix phpGH-17317: ResourceBundle crash on undefined iterator key.

ext/intl/resourcebundle/resourcebundle_iterator.c

@@ -105,7 +105,12 @@ static void resourcebundle_iterator_key( zend_object_iterator *iter, zval *key )
 	}
 
 	if (iterator->is_table) {
-		ZVAL_STRING(key, iterator->currentkey);
+		if (EXPECTED(iterator->currentkey)) {
+			ZVAL_STRING(key, iterator->currentkey);
+		} else {
+			ZVAL_NULL(key);
+			ZVAL_NULL(&iterator->current);
+		}
 	} else {
 		ZVAL_LONG(key, iterator->i);
 	}

ext/intl/tests/gh17317.phpt

@@ -0,0 +1,48 @@
+--TEST--
+GH-17319 (ResourceBundle iterator crash on NULL key)
+--EXTENSIONS--
+intl
+--CREDITS--
+KidFlo
+--FILE--
+<?php
+foreach ((new ResourceBundle('', NULL))->get('calendar')->get('buddhist') as $key => $value) {
+	echo "KEY: "; var_dump($key);
+	echo "VALUE: "; var_dump($value);
+}
+?>
+--EXPECT--
+KEY: string(15) "AmPmMarkersAbbr"
+VALUE: object(ResourceBundle)#3 (0) {
+}
+KEY: string(15) "AmPmMarkersAbbr"
+VALUE: object(ResourceBundle)#4 (0) {
+}
+KEY: string(16) "DateTimePatterns"
+VALUE: object(ResourceBundle)#3 (0) {
+}
+KEY: NULL
+VALUE: NULL
+KEY: NULL
+VALUE: NULL
+KEY: string(11) "appendItems"
+VALUE: object(ResourceBundle)#3 (0) {
+}
+KEY: string(16) "availableFormats"
+VALUE: object(ResourceBundle)#4 (0) {
+}
+KEY: string(8) "dayNames"
+VALUE: object(ResourceBundle)#3 (0) {
+}
+KEY: string(4) "eras"
+VALUE: object(ResourceBundle)#4 (0) {
+}
+KEY: string(15) "intervalFormats"
+VALUE: object(ResourceBundle)#3 (0) {
+}
+KEY: string(10) "monthNames"
+VALUE: object(ResourceBundle)#4 (0) {
+}
+KEY: string(8) "quarters"
+VALUE: object(ResourceBundle)#3 (0) {
+}