Don't warp the mouse for relative mode when the window doesn't have focus

src/events/SDL_mouse.c

@@ -358,7 +358,9 @@ SDL_PrivateSendMouseMotion(SDL_Window * window, SDL_MouseID mouseID, int relativ
             mouse->last_y = center_y;
             return 0;
         }
-        SDL_WarpMouseInWindow(window, center_x, center_y);
+        if (window && (window->flags & SDL_WINDOW_INPUT_FOCUS) != 0) {
+            SDL_WarpMouseInWindow(window, center_x, center_y);
+        }
     }
 
     if (relative) {

src/video/windows/SDL_windowsevents.c

@@ -663,7 +663,8 @@ WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
                 if (GetMouseMessageSource() != SDL_MOUSE_EVENT_SOURCE_TOUCH &&
                     lParam != data->last_pointer_update) {
                     SDL_SendMouseMotion(data->window, 0, 0, GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam));
-                    if (isWin10FCUorNewer && mouse->relative_mode_warp) {
+                    if (isWin10FCUorNewer && mouse->relative_mode_warp &&
+                        (data->window->flags & SDL_WINDOW_INPUT_FOCUS)) {
                         /* To work around #3931, Win10 bug introduced in Fall Creators Update, where
                            SetCursorPos() (SDL_WarpMouseInWindow()) doesn't reliably generate mouse events anymore,
                            after each windows mouse event generate a fake event for the middle of the window