memory leakage

[smutahoang]

https://github.com/tangjianpku/LINE/blob/5e32b41bfcec1269c434b383056ea205cf021e2d/linux/line.cpp#L256

when k == neg_table_size -1, it might be the case vid == num_vertices but por < 1 (it might be 0.99999 but not 1.0 due the machine epsilon), hence the next cur_sum computation is called which accesses the (num_vertices)-th elements of the vextex array -- which is out-of-range.