overlap between a point and a segment is broken

[golobor]

A working example:

In [15]: df_point = pd.DataFrame([['chr1', 1, 1]], columns=['chrom','start','end'])

In [16]: df_segment = pd.DataFrame([['chr1', 1, 2]], columns=['chrom','start','end'])

In [17]: bioframe.overlap(df_segment, df_point)
Out[17]:
  chrom  start  end chrom_  start_  end_
0  chr1      1    2   chr1       1     1

In [18]: bioframe.overlap(df_point, df_segment)
Out[18]:
  chrom  start  end chrom_  start_  end_
0  chr1      1    1   None    <NA>  <NA>

In [19]: bioframe.overlap(df_point, df_point)
Out[19]:
  chrom  start  end chrom_  start_  end_
0  chr1      1    1   None    <NA>  <NA>

This bug further causes bugs when subtracting segments from points.