[Patch 1.5] singlePar with non wide inset optimization

[Abdelrazak Younes]

Hi Juergen,

I have backported this fix from trunk. It is safe IMO and should go in 
1.5.2.

Abdel.
Index: BufferView.cpp
===================================================================
--- BufferView.cpp      (revision 20564)
+++ BufferView.cpp      (working copy)
@@ -1482,13 +1482,19 @@
 
        // If the paragraph metrics has changed, we can not
        // use the singlepar optimisation.
-       if (singlepar
+       if (singlepar) {
+               pit_type const bottom_pit = cursor_.bottom().pit();
+               int old_height = tm.parMetrics(bottom_pit).height();
                // In Single Paragraph mode, rebreak only
                // the (main text, not inset!) paragraph containing the cursor.
                // (if this paragraph contains insets etc., rebreaking will
                // recursively descend)
-               && tm.redoParagraph(cursor_.bottom().pit()))
-               singlepar = false;
+               tm.redoParagraph(bottom_pit);
+               // Paragraph height has changed so we cannot proceed to
+               // the singlePar optimisation.
+               if (tm.parMetrics(bottom_pit).height() != old_height)
+                       singlepar = false;
+       }
 
        pit_type const pit = anchor_ref_;
        int pit1 = pit;