Qt: correctly destroy EPG dialog

(cherry picked from commit 3273505a50f62e15dab7b6c328e940d456f2a07e)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/gui/qt4/dialogs_provider.cpp

@@ -97,6 +97,7 @@ DialogsProvider::~DialogsProvider()
     UpdateDialog::killInstance();
 #endif
     PluginDialog::killInstance();
+    EpgDialog::killInstance();
 
     delete menusMapper;
     delete menusUpdateMapper;