Deleting a single or multiple material shader nodes with enabled BI rendered mode leads to crash in blender with heap-use-after-free.

Steps to reproduce:
1) Ctrl+Left
2) Enable BI Rendered mode
3) Switch node editor into Material Shaders mode
4) Enable material shaders and press Delete -> heap-use-after-free

Tested with r58123 (that means ticket locks does not solve this problem (yet)).