Fixed problems with reassigning the already assigned attribute, see #9567.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@54245 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/grid.cpp

@@ -83,10 +83,12 @@ struct wxGridCellWithAttr
     wxGridCellWithAttr& operator=(const wxGridCellWithAttr& other)
     {
         coords = other.coords;
-        attr->DecRef();
-        attr = other.attr;
-        attr->IncRef();
-
+        if (attr != other.attr)
+        {
+            attr->DecRef();
+            attr = other.attr;
+            attr->IncRef();
+        }
         return *this;
     }
 
@@ -2760,13 +2762,20 @@ void wxGridRowOrColAttrData::SetAttr(wxGridCellAttr *attr, int rowOrCol)
     int i = m_rowsOrCols.Index(rowOrCol);
     if ( i == wxNOT_FOUND )
     {
-        // add the attribute
-        m_rowsOrCols.Add(rowOrCol);
-        m_attrs.Add(attr);
+        if ( attr )
+        {
+            // add the attribute
+            m_rowsOrCols.Add(rowOrCol);
+            m_attrs.Add(attr);
+        }
+        // nothing to remove
     }
     else
     {
         size_t n = (size_t)i;
+        if ( m_attrs[n] == attr )
+            // nothing to do
+            return; 
         if ( attr )
         {
             // change the attribute