CORE-4182 Fix for reselecting folder in DiskResourcePresenterImpl.

Updated the DiskResourcePresenterImpl::setSelectedFolderById method to de-select the currently selected folder, in case it is the same as folderToSelect, in order to load the center panel.
The go(HasOneWidget) method will now call setSelectedFolderById, which is null-safe, with getSelectedFolder() in order to accomplish the same thing.