Fix panic when no keys present for srl node

[hellt]

No description provided.

[codecov]

Codecov Report

Merging #1604 (594f913) into main (f2b4a62) will decrease coverage by 0.02%.
Report is 2 commits behind head on main.
The diff coverage is 73.33%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1604      +/-   ##
==========================================
- Coverage   48.59%   48.58%   -0.02%     
==========================================
  Files         133      133              
  Lines       12789    12798       +9     
==========================================
+ Hits         6215     6218       +3     
- Misses       5870     5874       +4     
- Partials      704      706       +2     

Files Changed	Coverage Δ
nodes/srl/srl.go	57.07% <0.00%> (ø)
nodes/srl/sshkey.go	88.88% <78.57%> (-11.12%)	⬇️

... and 2 files with indirect coverage changes