fix: preemptively fix potential issue with infinite loop

in cases where the number of remaining candidates is lower than the number of vacancies, it is
possible that the program gets into an infinite loop

example/tests/out.txt

@@ -1,3 +1,3 @@
 Enter the number of vacancies: Enter the number of votes: Enter the number of candidates: Enter the names of the candidates (space-separated): Enter the ballots (space-/line-separated): 
 
-Elected candidates: JoseBishop AntonyMorrow JadenWall VanessaPacheco 
+Elected candidates: JoseBishop JadenWall AntonyMorrow VanessaPacheco 

src/hare-clark.hpp

@@ -75,7 +75,7 @@ class HareClark {
     std::vector<double> votes(candidates.size()); // Current value of votes for each candidate
     for (const auto& [ballot, weight] : ballots_with_weights) votes[ballot.back()] += weight;
 
-    while (number_of_vacancies) {
+    while (number_of_vacancies < candidates.size() - unavailable_candidates.size()) {
       int winner = -1;
       int loser = -1;
       for (int i = 0; i < candidates.size(); ++i) {
@@ -97,6 +97,9 @@ class HareClark {
         votes[loser] = -1;
       }
     }
+    if (number_of_vacancies) {
+      for (int i = 0; i < candidates.size(); ++i) if (!unavailable_candidates.count(i)) elected_candidates.push_back(candidates[i]);
+    }
     return elected_candidates;
   }
 };