Remove a sometimes blocked call to dispatch

Remove a sometimes blocked call to dispatch

Dispatching LFUN_BUFFER_ZOOM inside of GuiView::restoreLayout() was
blocked in some cases because the function can be called without a
buffer (and the LFUN is marked as needing a buffer). Instead of
conditioning on a buffer, the call is removed because in testing it
does not appear why it is needed.

This commit removes the status message that is displayed if starting
LyX without opening a buffer:

    "Command not allowed without any document open"

See discussion at:

    https://www.mail-archive.com/search?l=mid&q=20170718084344.3kjmu7hzoyajt7vd%40steph

This commit amends 4183a9f4.