Extensions: fix Qt freeze when reloading scripts

Description of the bug:

 This freeze happened only on Windows (tested on XP & Wine), but not on
 Linux. If I only moved up the "killInstance()" line, then the freeze
 would happen only on Linux but not on Windows.
 In these cases the QDialog's destructor never returned.
(cherry picked from commit 06e609ea922918f4d2d0f427049a236b4a4c08af)
Signed-off-by: Pierre Ynard <linkfanel@yahoo.fr>

modules/gui/qt4/dialogs/extensions.cpp

@@ -207,11 +207,6 @@ ExtensionDialog::ExtensionDialog( intf_thread_t *_p_intf,
 ExtensionDialog::~ExtensionDialog()
 {
     msg_Dbg( p_intf, "Deleting extension dialog '%s'", qtu(windowTitle()) );
-    /* Delete all widgets */
-    extension_widget_t *p_widget;
-    p_dialog->b_kill = true;
-    p_dialog->p_sys_intf = NULL;
-    vlc_cond_signal( &p_dialog->cond );
 }
 
 QWidget* ExtensionDialog::CreateWidget( extension_widget_t *p_widget )

modules/gui/qt4/extensions_manager.cpp

@@ -118,11 +118,10 @@ void ExtensionsManager::unloadExtensions()
     if( !p_extensions_manager )
         return;
     b_unloading = true;
+    ExtensionsDialogProvider::killInstance();
     module_unneed( p_extensions_manager, p_extensions_manager->p_module );
     vlc_object_release( p_extensions_manager );
     p_extensions_manager = NULL;
-    emit extensionsUpdated();
-    ExtensionsDialogProvider::killInstance();
 }
 
 void ExtensionsManager::reloadExtensions()