fixes gap issue

testable with:
==> a.bed <==
chr1	1	10
chr1	50	60

==> b.bed <==
chr1	1	20
chr1	30	40
chr1	50	60

==> c.bed <==
chr1	1	20
chr1	30	40
chr1	50	60

==> result <==
chr1	1	20
chr1	30	40
chr1	50	60

==> previous result <==
no peaks
loop optimization
Merge pull request #1 from brwnj/bugfix_combine_peaks

fixes gap issue