fix: louvain.c first_stage Ids array initial value error

[MikuSugar]

In the first_stage function, the ids array is assigned to lv->clen. The array will cross the boundary, and lv->nlen should be assigned. (first_stage 函数 中 ids 数组赋予 lv->clen 会出现数组越界，应该赋予 lv->nlen)