dual boundary class can have a bad pair

[gchi-bas]

Describe the bug
When running the vorticity pairing with a dual boundary class, it failed when a 'pair' was established with a good OCB and an EAB index outside of the data range.

To Reproduce
Steps to reproduce the behavior:

stime = dt.datetime(2000,1,1)
etime = dt.datetime(2005,1,1)
dual = ocbpy.DualBoundary(stime=stime, etime=etime, hemisphere=1)
vort2ascii_ocb(blah)

Fails at 2002-10-31 20:05:16

Expected behavior
Create a data file with dual boundary coordinates

Desktop (please complete the following information):

• OS: Linux
• Python version: 3.12
• Other relevant details of your set up