unitigger segfaults

[imranfanaswala]

Hello,

'tigger' segfaults on the attached FASTA file (rename the file to .png). Here are the commands:

nucmer -maxmatch -c 40 sample.fa sample.fa -p sample
show-coords -H -c -l -o -r sample.delta | nucmerAnnotate -ignore 180 | egrep 'BEGIN|END|CONTAIN|IDENTITY' > sample.coords
nucmer2ovl -ignore 180 -tab sample.coords | sort2 > sample.ovl
ovl2OVL sample.ovl > sample.OVL
toAmos -o sample.afg -s sample.fa
bank-transact -c -z -b sample.bnk -m sample.afg
bank-transact    -z -b sample.bnk -m sample.OVL
tigger -v 3 -g -b sample.bnk
![sample](https://cloud.githubusercontent.com/assets/422028/7638044/763d9414-fa72-11e4-8fbe-813602f61eca.png)

The stack trace shows: #0 Graph::new_edge (this=0x87e1048, p_n1=0x87e8260, p_n2=0x0, p_element=0x87e8bf0) at Graph.cc:217

217 p_n2->add_iedge(e);