destroy: fix folder as topology ref

[steiler]

fixing #1745

[codecov]

Codecov Report

Merging #1747 (0f50831) into main (ab128e4) will decrease coverage by 0.08%.
The diff coverage is 84.21%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1747      +/-   ##
==========================================
- Coverage   51.97%   51.89%   -0.08%     
==========================================
  Files         144      144              
  Lines       13961    13964       +3     
==========================================
- Hits         7256     7247       -9     
- Misses       5893     5902       +9     
- Partials      812      815       +3     

Files	Coverage Δ
clab/config.go	66.58% <ø> (-0.26%)	⬇️
types/topo_paths.go	69.67% <100.00%> (+0.25%)	⬆️
clab/clab.go	76.67% <90.32%> (+0.08%)	⬆️
cmd/destroy.go	66.50% <25.00%> (-1.00%)	⬇️

... and 2 files with indirect coverage changes

[hellt]

Thanks @steiler!