Stop struct_learn when there are no more candidates for transformation

[RenatoGeh]

This is the LogicCircuits side of Tractables/ProbabilisticCircuits.jl#50.

[codecov]

Codecov Report

Merging #68 (a83cfe1) into master (3fc4328) will decrease coverage by 2.03%.
The diff coverage is 94.11%.

@@            Coverage Diff             @@
##           master      #68      +/-   ##
==========================================
- Coverage   85.89%   83.85%   -2.04%     
==========================================
  Files          29       29              
  Lines        2396     2410      +14     
==========================================
- Hits         2058     2021      -37     
- Misses        338      389      +51     

Impacted Files	Coverage Δ
src/transformations.jl	95.21% <94.11%> (-0.12%)	⬇️
src/Utils/cubitvector.jl	28.57% <0.00%> (-18.10%)	⬇️
src/Utils/data.jl	65.66% <0.00%> (-14.46%)	⬇️
src/satisfies_flow.jl	47.45% <0.00%> (-7.46%)	⬇️
src/bit_circuit.jl	78.84% <0.00%> (-1.93%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 3fc4328...c775c62. Read the comment docs.