Restore selected window after killing vundo buffer

[wyuenho]

It is not always the case that Emacs will select the original buffer's window after killing the vundo buffer and window, this is especially true when using a window manager such as windows-purpose. This PR makes sure the original buffer's window is reselected after killing vundo's window.

[ideasman42]

While this seems reasonable select-window check check if the window is nil before calling as there is a small possibility no window can be found for the buffer.

[wyuenho]

done

[casouri]

Thanks! Could you merge the two commits and force push? Then I can edit the commit message to comply to GNU format.

[wyuenho]

done

[casouri]

Merged, thanks!