Arista: fix a crash when using source nat on an interface with no IP address

[dhalperi]

No description provided.

[batfish-bot]

This change is 

[progwriter]

Reviewed 3 of 3 files at r1.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @anothermattbrown)

[progwriter]

Reviewed 1 of 1 files at r2.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @anothermattbrown)

[codecov]

Codecov Report

Merging #6107 into master will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master    #6107      +/-   ##
============================================
- Coverage     72.70%   72.68%   -0.02%     
+ Complexity    34636    34634       -2     
============================================
  Files          2815     2815              
  Lines        141279   141308      +29     
  Branches      16966    16970       +4     
============================================
+ Hits         102713   102716       +3     
- Misses        30410    30424      +14     
- Partials       8156     8168      +12     

Impacted Files	Coverage Δ	Complexity Δ
...ish/representation/arista/AristaConfiguration.java	53.62% <100.00%> (+0.09%)	157.00 <3.00> (+1.00)
...stion/searchroutepolicies/BgpRouteConstraints.java	91.83% <0.00%> (-8.17%)	14.00% <0.00%> (+6.00%)	⬇️
.../org/batfish/dataplane/rib/RouteAdvertisement.java	84.78% <0.00%> (-4.35%)	16.00% <0.00%> (-1.00%)
...c/main/java/org/batfish/dataplane/rib/RibTree.java	89.58% <0.00%> (-4.17%)	27.00% <0.00%> (-1.00%)
...rc/main/java/org/batfish/datamodel/flow/Trace.java	87.09% <0.00%> (-3.23%)	12.00% <0.00%> (-1.00%)
...col/src/main/java/org/batfish/role/InferRoles.java	89.09% <0.00%> (-1.82%)	49.00% <0.00%> (-2.00%)
...src/main/java/org/batfish/coordinator/PoolMgr.java	59.25% <0.00%> (-1.24%)	15.00% <0.00%> (-1.00%)
...ain/java/org/batfish/storage/FileBasedStorage.java	86.55% <0.00%> (-0.66%)	257.00% <0.00%> (ø%)
...src/main/java/org/batfish/coordinator/WorkMgr.java	77.01% <0.00%> (-0.54%)	283.00% <0.00%> (-2.00%)
...rg/batfish/dataplane/ibdp/EigrpRoutingProcess.java	92.72% <0.00%> (-0.39%)	68.00% <0.00%> (-1.00%)
... and 5 more