Fix memory leak in wxGridSizer::Insert() if an assert in it fails

This avoids another memory leak in the test suite, which intentionally
triggers an assert in this function.

src/common/sizer.cpp

@@ -32,6 +32,7 @@
 #include "wx/vector.h"
 #include "wx/listimpl.cpp"
 #include "wx/private/window.h"
+#include "wx/scopedptr.h"
 
 
 //---------------------------------------------------------------------------
@@ -1479,6 +1480,9 @@ wxGridSizer::wxGridSizer( int rows, int cols, const wxSize& gap )
 
 wxSizerItem *wxGridSizer::DoInsert(size_t index, wxSizerItem *item)
 {
+    // Ensure that the item will be deleted in case of exception.
+    wxScopedPtr<wxSizerItem> scopedItem( item );
+
     // if only the number of columns or the number of rows is specified for a
     // sizer, arbitrarily many items can be added to it but if both of them are
     // fixed, then the sizer can't have more than that many items -- check for
@@ -1519,7 +1523,7 @@ wxSizerItem *wxGridSizer::DoInsert(size_t index, wxSizerItem *item)
         );
     }
 
-    return wxSizer::DoInsert(index, item);
+    return wxSizer::DoInsert( index, scopedItem.release() );
 }
 
 int wxGridSizer::CalcRowsCols(int& nrows, int& ncols) const