[LyX/master] Fix bug #8884: Crash when "navigate to next change"

[Jean-Marc Lasgouttes]

commit c98ce56a03411021152b340bdb418d4d01d61548
Author: Jean-Marc Lasgouttes <lasgout...@lyx.org>
Date:   Fri Sep 27 10:47:36 2013 +0200

    Fix bug #8884: Crash when "navigate to next change"
    
    The two fixes here a obviously right, although it is not clear why they are 
sufficient to fix the bug. Anyway I cannot reproduce any crash with it.
    
     * the first part just conditions a whole if/else to 
change_next_pos.changed(). Originally, only the if branch was concerned.
    
     * the second part is to avoid calling CursorSlice::backwardPos() when 
position is 0. Doing this leads to an assertion.

diff --git a/src/lyxfind.cpp b/src/lyxfind.cpp
index a1cab4c..ca43d47 100644
--- a/src/lyxfind.cpp
+++ b/src/lyxfind.cpp
@@ -419,21 +419,24 @@ bool findChange(BufferView * bv, bool next)
        // of this function). This will avoid changes to be selected half.
        bool search_both_sides = false;
        Cursor tmpcur = cur;
-       // Leave math first
+       // Find enclosing text cursor
        while (tmpcur.inMathed())
                tmpcur.pop_back();
        Change change_next_pos
                = tmpcur.paragraph().lookupChange(tmpcur.pos());
-       if (change_next_pos.changed() && cur.inMathed()) {
-               cur = tmpcur;
-               search_both_sides = true;
-       } else if (tmpcur.pos() > 0 && tmpcur.inTexted()) {
-               Change change_prev_pos
-                       = tmpcur.paragraph().lookupChange(tmpcur.pos() - 1);
-               if (change_next_pos.isSimilarTo(change_prev_pos))
+       if (change_next_pos.changed()) {
+               if (cur.inMathed()) {
+                       cur = tmpcur;
                        search_both_sides = true;
+               } else if (tmpcur.pos() > 0 && tmpcur.inTexted()) {
+                       Change change_prev_pos
+                               = tmpcur.paragraph().lookupChange(tmpcur.pos() 
- 1);
+                       if (change_next_pos.isSimilarTo(change_prev_pos))
+                               search_both_sides = true;
+               }
        }
 
+       // find the next change
        if (!findChange(cur, next))
                return false;
 
@@ -441,7 +444,7 @@ bool findChange(BufferView * bv, bool next)
 
        CursorSlice & tip = cur.top();
 
-       if (!next)
+       if (!next && tip.pos() > 0)
                // take a step into the change
                tip.backwardPos();