Correctly update run_scheduler_at when scheduler didn't run.

In some cases the scheduler does not have to run. In such
cases the SchedulerStats.algorithm_runtime_ is set max_uint64.
Previously, the code was directly using algorithm_runtime_ and
coulse cause integer overflow. This change addresses this issue.

Affected modules: sim

Change-Id: I065ac766f646c7d2d1b2d6549c80405cd300bd53

src/sim/simulator.cc

@@ -208,8 +208,15 @@ uint64_t Simulator::ScheduleJobsHelper(uint64_t run_scheduler_at) {
         return event_manager_->GetTimeOfNextSchedulerRun(
             run_scheduler_at, scheduler_stats.scheduler_runtime_);
       } else {
-        return event_manager_->GetTimeOfNextSchedulerRun(
-            run_scheduler_at, scheduler_stats.algorithm_runtime_);
+        if (scheduler_stats.algorithm_runtime_ ==
+            numeric_limits<uint64_t>::max()) {
+          // Scheduler hasn't executed.
+          return event_manager_->GetTimeOfNextSchedulerRun(
+                     run_scheduler_at, 0);
+        } else {
+          return event_manager_->GetTimeOfNextSchedulerRun(
+                     run_scheduler_at, scheduler_stats.algorithm_runtime_);
+        }
       }
     } else if (FLAGS_solver_runtime_accounting_mode == "solver") {
       return event_manager_->GetTimeOfNextSchedulerRun(