[Bf-codereview] Custom Nodes (issue 7099061)

[brechtvanlommel at gmail.com]

Opening this file causes a crash with the patch applied.
http://projects.blender.org/tracker/download.php/9/498/33896/23575/pm_bug.blend

0   blender                             0x000000010e58784c
blender_crash_handler + 412
1   libsystem_c.dylib                   0x00007fff8b0228ea _sigtramp +
26
2   ???                                 0xfffffffffffffff0 0x0 +
18446744073709551600
3   blender                             0x000000010eb381fc
node_group_input_init + 44
4   blender                             0x000000010ea9d42b nodeAddNode +
459
5   blender                             0x000000010eb64742 do_versions +
12274
6   blender                             0x000000010eb76096
blo_read_file_internal + 2518

https://codereview.appspot.com/7099061/