Bugfix: Edit button was not switched off when opening a new image

Reported in issue #2239 :
https://github.com/Beep6581/RawTherapee/issues/2239#issuecomment-521955110

rtgui/editorpanel.cc

@@ -1090,8 +1090,8 @@ void EditorPanel::close ()
         if (iareapanel) {
             iareapanel->imageArea->setPreviewHandler (nullptr);
             iareapanel->imageArea->setImProcCoordinator (nullptr);
-            iareapanel->imageArea->unsubscribe();
         }
+        tpc->editModeSwitchedOff();
 
         rtengine::StagedImageProcessor::destroy (ipc);
         ipc = nullptr;