Ensure that there is a modal event loop before trying to use it.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69704 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/osx/cocoa/evtloop.mm

@@ -421,6 +421,7 @@ void wxWindowDisabler::DoDisable(wxWindow *winToSkip)
     }
     
     m_modalEventLoop = (wxEventLoop*)wxEventLoopBase::GetActive();
+    if (m_modalEventLoop)
         m_modalEventLoop->BeginModalSession(winToSkip);
 }
 
@@ -429,6 +430,7 @@ wxWindowDisabler::~wxWindowDisabler()
     if ( !m_disabled )
         return;
     
+    if (m_modalEventLoop)
         m_modalEventLoop->EndModalSession();
     
     wxWindowList::compatibility_iterator node;