Treat 0xffff the same as 0 for the handle generation field to avoid

dlls/user/win.c

@@ -307,13 +307,14 @@ WND *WIN_GetPtr( HWND hwnd )
     USER_Lock();
     if ((ptr = user_handles[index]))
     {
-        if (ptr->dwMagic == WND_MAGIC && (!HIWORD(hwnd) || hwnd == ptr->hwndSelf))
+        if (ptr->dwMagic == WND_MAGIC &&
+            (hwnd == ptr->hwndSelf || !HIWORD(hwnd) || HIWORD(hwnd) == 0xffff))
             return ptr;
         ptr = NULL;
     }
     else if (index == USER_HANDLE_TO_INDEX(hwndDesktop))
     {
-        if (!HIWORD(hwnd) || hwnd == GetDesktopWindow()) ptr = WND_DESKTOP;
+        if (hwnd == GetDesktopWindow() || !HIWORD(hwnd) || HIWORD(hwnd) == 0xffff) ptr = WND_DESKTOP;
         else ptr = NULL;
     }
     else ptr = WND_OTHER_PROCESS;

server/user.c

@@ -35,12 +35,14 @@ static int allocated_handles;
 
 static struct user_handle *handle_to_entry( user_handle_t handle )
 {
+    unsigned short generation;
     int index = (((unsigned int)handle & 0xffff) - FIRST_USER_HANDLE) >> 1;
     if (index < 0 || index >= nb_handles) return NULL;
     if (!handles[index].type) return NULL;
-    if (((unsigned int)handle >> 16) && ((unsigned int)handle >> 16 != handles[index].generation))
-        return NULL;
+    generation = (unsigned int)handle >> 16;
+    if (generation == handles[index].generation || !generation || generation == 0xffff)
         return &handles[index];
+    return NULL;
 }
 
 inline static user_handle_t entry_to_handle( struct user_handle *ptr )