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.

src/frontends/qt4/GuiView.cpp

@@ -773,7 +773,6 @@ bool GuiView::restoreLayout()
 {
 	QSettings settings;
 	lyxrc.currentZoom = settings.value("zoom", lyxrc.zoom).toInt();
-	lyx::dispatch(FuncRequest(LFUN_BUFFER_ZOOM, convert<docstring>(lyxrc.currentZoom)));
 	devel_mode_ = settings.value("devel_mode", devel_mode_).toBool();
 	settings.beginGroup("views");
 	settings.beginGroup(QString::number(id_));