Discard counters for out-of-bounds levels

Previously this just crashed.

zapcore/sampler.go

@@ -197,12 +197,14 @@ func (s *sampler) Check(ent Entry, ce *CheckedEntry) *CheckedEntry {
 		return ce
 	}
 
-	counter := s.counts.get(ent.Level, ent.Message)
-	n := counter.IncCheckReset(ent.Time, s.tick)
-	if n > s.first && (n-s.first)%s.thereafter != 0 {
-		s.hook(ent, LogDropped)
-		return ce
+	if ent.Level >= _minLevel && ent.Level <= _maxLevel {
+		counter := s.counts.get(ent.Level, ent.Message)
+		n := counter.IncCheckReset(ent.Time, s.tick)
+		if n > s.first && (n-s.first)%s.thereafter != 0 {
+			s.hook(ent, LogDropped)
+			return ce
+		}
+		s.hook(ent, LogSampled)
 	}
-	s.hook(ent, LogSampled)
 	return s.Core.Check(ent, ce)
 }

zapcore/sampler_test.go

@@ -224,3 +224,9 @@ func TestSamplerRaces(t *testing.T) {
 	close(start)
 	wg.Wait()
 }
+
+func TestSamplerBounds(t *testing.T) {
+	// Prove that out-of-bounds levels don't crash.
+	sampler, _ := fakeSampler(DebugLevel-1, time.Minute, 2, 3)
+	writeSequence(sampler, 1, DebugLevel-1)
+}