fix(server): Prevent crash from dangling pointers in file dialog map

Fixed two bugs when closing ScreenSpyDlg with file transfer dialogs:

1. Access violation (0xC0000005): CDlgFileSend self-destructs via
   PostNcDestroy (delete this) when closed, leaving dangling pointers
   in m_FileRecvDlgs map.

2. Double-free: Original code called DestroyWindow() then delete,
   but DestroyWindow already triggers delete this via PostNcDestroy.

Solution:
- Store {HWND, pointer} pairs instead of raw pointers
- Check HWND validity with IsWindow() before accessing pointer
- Use SendMessage(WM_CLOSE) to let dialog self-destruct safely
- Always erase map entries to prevent accumulation of invalid data

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

server/2015Remote/ScreenSpyDlg.cpp

@@ -238,10 +238,14 @@ CScreenSpyDlg::~CScreenSpyDlg()
     StopAudioPlayback();
 
     // 清理所有文件接收对话框
-    for (auto& pair : m_FileRecvDlgs) {
-        if (pair.second) {
-            pair.second->DestroyWindow();
-            delete pair.second;
+    // 注意：对话框可能已经被用户关闭并自我销毁（PostNcDestroy 中 delete this）
+    // 存储了 HWND 用于安全检查，避免访问野指针
+    for (auto& entry : m_FileRecvDlgs) {
+        HWND hWnd = entry.second.first;
+        if (hWnd && ::IsWindow(hWnd)) {
+            // 通过 HWND 同步发送关闭消息，确保对话框在析构前完全关闭
+            // 使用 SendMessage 而非 PostMessage，避免异步问题
+            ::SendMessage(hWnd, WM_CLOSE, 0, 0);
         }
     }
     m_FileRecvDlgs.clear();
@@ -861,13 +865,15 @@ LRESULT CScreenSpyDlg::OnRecvFileV2Chunk(WPARAM wParam, LPARAM lParam)
     uint64_t transferID = msgData->transferID;
 
     // 创建或获取进度对话框（按 transferID 管理）
-    CDlgFileSend*& dlg = m_FileRecvDlgs[transferID];
-    if (dlg == nullptr) {
+    auto& entry = m_FileRecvDlgs[transferID];
+    CDlgFileSend* dlg = entry.second;
+    if (dlg == nullptr || !::IsWindow(entry.first)) {
         dlg = new CDlgFileSend(m_pParent, m_ContextObject->GetServer(), m_ContextObject, FALSE);
         dlg->Create(IDD_DIALOG_FILESEND, GetDesktopWindow());
         dlg->SetWindowTextA(_TR("接收文件"));
         dlg->ShowWindow(SW_SHOW);
         dlg->m_bKeepConnection = TRUE;  // 不断开连接
+        entry = { dlg->GetSafeHwnd(), dlg };
     }
 
     // 接收文件
@@ -910,7 +916,11 @@ LRESULT CScreenSpyDlg::OnRecvFileV2Complete(WPARAM wParam, LPARAM lParam)
     // 关闭进度对话框
     auto it = m_FileRecvDlgs.find(transferID);
     if (it != m_FileRecvDlgs.end()) {
-        it->second->FinishFileSend(verifyOk);
+        // 只有窗口有效时才调用 FinishFileSend
+        if (::IsWindow(it->second.first)) {
+            it->second.second->FinishFileSend(verifyOk);
+        }
+        // 无论窗口是否有效，都要移除条目（避免累积无效条目）
         m_FileRecvDlgs.erase(it);
     }
 

server/2015Remote/ScreenSpyDlg.h

@@ -198,7 +198,8 @@ public:
 
     // 文件接收进度对话框（用于 Linux Ctrl+C -> 服务端 Ctrl+V）
     // 按 transferID 管理多个并发传输
-    std::map<uint64_t, class CDlgFileSend*> m_FileRecvDlgs;
+    // 存储 {HWND, 指针} 对，HWND 用于安全检查（指针可能变成野指针）
+    std::map<uint64_t, std::pair<HWND, class CDlgFileSend*>> m_FileRecvDlgs;
 
     void SaveSnapshot(void);
     // 对话框数据