Ignore unknown WM_SIZE types.

According to MSDN, we can also get SIZE_MAXHIDE and SIZE_MAXSHOW,
based on state changes to other windows. It's not clear under
what circumstances this will happen (I saw some docs indicating
it may require multiple application windows), but it doesn't seem
right to treat them as RESTORED.

src/video/windows/SDL_windowsevents.c

@@ -1167,10 +1167,12 @@ WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
                 SDL_SendWindowEvent(data->window,
                     SDL_WINDOWEVENT_MINIMIZED, 0, 0);
                 break;
-            default:
+            case SIZE_RESTORED:
                 SDL_SendWindowEvent(data->window,
                     SDL_WINDOWEVENT_RESTORED, 0, 0);
                 break;
+            default:
+                break;
             }
         }
         break;