ext/session: Preserve handler recursion guard

ext/session/mod_user.c

@@ -27,7 +27,6 @@ static void ps_call_handler(zval *func, int argc, zval *argv, zval *retval)
 {
 	int i;
 	if (PS(in_save_handler)) {
-		PS(in_save_handler) = 0;
 		ZVAL_UNDEF(retval);
 		php_error_docref(NULL, E_WARNING, "Cannot call session save handler in a recursive manner");
 	} else {

ext/session/tests/user_session_module/session_handler_recursion_gc.phpt

@@ -0,0 +1,61 @@
+--TEST--
+session_gc() calls rejected recursively from SessionHandler::write() remain rejected
+--INI--
+session.save_path=
+session.name=PHPSESSID
+--EXTENSIONS--
+session
+--FILE--
+<?php
+class Handler extends SessionHandler
+{
+    public int $gcCalls = 0;
+
+    public function open(string $path, string $name): bool
+    {
+        return true;
+    }
+
+    public function close(): bool
+    {
+        return true;
+    }
+
+    public function read(string $id): string|false
+    {
+        return '';
+    }
+
+    public function write(string $id, string $data): bool
+    {
+        var_dump(session_gc());
+        var_dump(session_gc());
+        return true;
+    }
+
+    public function destroy(string $id): bool
+    {
+        return true;
+    }
+
+    public function gc(int $maxLifetime): int|false
+    {
+        $this->gcCalls++;
+        return 0;
+    }
+}
+
+$handler = new Handler();
+session_set_save_handler($handler, true);
+session_start();
+$_SESSION['key'] = 'value';
+session_write_close();
+var_dump($handler->gcCalls);
+?>
+--EXPECTF--
+Warning: session_gc(): Cannot call session save handler in a recursive manner in %s on line %d
+bool(false)
+
+Warning: session_gc(): Cannot call session save handler in a recursive manner in %s on line %d
+bool(false)
+int(0)