Error if multiple reads mapped onto the region

I am having issues running rseg-diff where if different multiple reads are mapped to the same region, it's throwing error that it is not sorted.

```[LOADING_DATA] reads
ERROR: reads not sorted in CENH3_2C_allmerge_1M_sort.bed
1	28	129	NS500599:158:H55CVBGX5:1:21108:3468:1367/1	0	-
1	28	129	NS500599:159:HCHWVBGX5:2:12109:11569:19492/1	0	+
```