Assert that what might look like a possible division by zero is actually unreachable

src/bench/bench.cpp

@@ -92,6 +92,8 @@ bool benchmark::State::KeepRunning()
 
     --count;
 
+    assert(count != 0 && "count == 0 => (now == 0 && beginTime == 0) => return above");
+
     // Output results
     double average = (now-beginTime)/count;
     int64_t averageCycles = (nowCycles-beginCycles)/count;