Fixed a crash when deleting the last timer

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@38235 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/timer.cpp

@@ -190,7 +190,11 @@ void wxTimerScheduler::NotifyTimers()
                         QueueTimer(desc, now + desc->timer->GetInterval());
                 }
                 else
+                {
                     desc = m_timers;
+                    if (!desc)
+                        break;
+                }
             }
         }
     }