Fix binary search recursion error for preamble

[rewong03]

pub8\CdiacBundles\06AQ/06AQ20150818.tsv
pub8\CdiacBundles\33RO

[tskluzac]

[DO NOT CLOSE] I've put a bandaid on it, but it's not entirely fixed.

The issue is that something is allowing both the upper and lower bounds to fall beneath the current row (and converge to the same row). The bandaid is -- if upper-bound and lower-bound are both within 1 of the current_row, then return.

Not robust -- need to investigate the actual source of the problem.