Solver: No need to check previous decision if we reached the first one

src/Composer/DependencyResolver/Solver.php

@@ -417,6 +417,7 @@ class Solver
             }
             unset($literal);
 
+            if ($decisionId > 0) {
                 $decision = $this->decisions->atOffset($decisionId-1);
                 if ($rule !== $decision[Decisions::DECISION_REASON] && $decision[Decisions::DECISION_REASON] instanceof MultiConflictRule) {
                     $num++;
@@ -426,6 +427,7 @@ class Solver
                         }
                     }
                 }
+            }
 
             $l1retry = true;
             while ($l1retry) {