[LyX/master] Update all paragraphs layouts when undoing bufferparams

[Jean-Marc Lasgouttes]

commit 82b6dc8aa9c8f5f09d1b6643afd959d86bc4afa3
Author: Jean-Marc Lasgouttes <lasgout...@lyx.org>
Date:   Tue Jan 19 16:31:35 2016 +0100

    Update all paragraphs layouts when undoing bufferparams
    
    When undo restores a previous BufferParams instance, it should also
    update all the layout pointers in the document's paragraphs.
    
    Fixes #9916.

diff --git a/src/Undo.cpp b/src/Undo.cpp
index 7b924c7..143af4e 100644
--- a/src/Undo.cpp
+++ b/src/Undo.cpp
@@ -21,6 +21,8 @@
 #include "BufferParams.h"
 #include "buffer_funcs.h"
 #include "Cursor.h"
+#include "CutAndPaste.h"
+#include "ErrorList.h"
 #include "Paragraph.h"
 #include "ParagraphList.h"
 #include "Text.h"
@@ -29,6 +31,7 @@
 #include "mathed/MathData.h"
 
 #include "insets/Inset.h"
+#include "insets/InsetText.h"
 
 #include "support/debug.h"
 #include "support/gettext.h"
@@ -453,7 +456,13 @@ void Undo::Private::doTextUndoOrRedo(CursorData & cur, 
UndoElementStack & stack,
                // This is a params undo element
                delete otherstack.top().bparams;
                otherstack.top().bparams = new BufferParams(buffer_.params());
+               DocumentClassConstPtr olddc = 
buffer_.params().documentClassPtr();
                buffer_.params() = *undo.bparams;
+               // The error list is not supposed to be helpful here.
+               ErrorList el;
+               cap::switchBetweenClasses(olddc, 
buffer_.params().documentClassPtr(),
+                       static_cast<InsetText &>(buffer_.inset()), el);
+               LATTEST(el.empty());
        } else if (dit.inMathed()) {
                // We stored the full cell here as there is not much to be
                // gained by storing just 'a few' paragraphs (most if not