#1 fixes bug#1899884 -- Program cannot run even number of thrad

[Kov Chai]

hi Dr. Taku,

i found crf++ still assign a thread for a already freed tagger. that may lead to segment fault in multi-thread environment. a tiny patch is attached. thanks for your great work!

if (!_x->empty())
x.push_back(_x);
- else
+ else {
delete _x;
-
+ continue;
+ }
+
_x->set_thread_id(line % thread_num);

[Kov Chai]

continue if tagger has no X in it.