Crash on autosave

[Roman]

Crash happened on autosave.

Ubuntu 13.10 64 bit

Dump written 2014-2-27_17-8
Version: 1.5.2
Window: autosaver
Reason: function_clause

Short stack trace:
[]

Long stack trace:
[{gb_trees,get_1,[-5,nil],[{file,"gb_trees.erl"},{line,245}]},
{wings_we,'-do_renumber/3-lc$^0/1-0-',2,[{file,"wings_we.erl"},{line,677}]},
{wings_we,do_renumber,3,[{file,"wings_we.erl"},{line,677}]},
{wings_we,do_renumber,2,[{file,"wings_we.erl"},{line,642}]},
{wings_we,renumber,2,[{file,"wings_we.erl"},{line,257}]},
{wings_ff_wings,renumber,5,[{file,"wings_ff_wings.erl"},{line,679}]},
{wings_ff_wings,export,2,[{file,"wings_ff_wings.erl"},{line,616}]},
{wings_file,autosave,1,[{file,"wings_file.erl"},{line,577}]}]