Logic fix for the rounding heuristic of the Probability Simplex

[dhendryc]

In the hyperplane-aware rounding heuristic for the Probability Simplex, it can happen that the rounded point as all zero entries for the integer variables. In which case, we just return the point but let the feasibility check run.

[codecov]

Codecov Report

Attention: 18 lines in your changes are missing coverage. Please review.

Comparison is base (ee5cc6c) 86.23% compared to head (9145f03) 87.17%.
Report is 14 commits behind head on main.

Files	Patch %	Lines
src/polytope_blmos.jl	90.16%	6 Missing ⚠️
src/MOI_bounded_oracle.jl	87.50%	4 Missing ⚠️
src/callbacks.jl	50.00%	4 Missing ⚠️
src/heuristics.jl	96.15%	3 Missing ⚠️
src/node.jl	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #175      +/-   ##
==========================================
+ Coverage   86.23%   87.17%   +0.94%     
==========================================
  Files          17       18       +1     
  Lines        1482     1622     +140     
==========================================
+ Hits         1278     1414     +136     
- Misses        204      208       +4     

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