fix tests

weed/storage/needle_map_metric_test.go

@@ -16,7 +16,7 @@ func TestFastLoadingNeedleMapMetrics(t *testing.T) {
 
 	for i := 0; i < 10000; i++ {
 		nm.Put(Uint64ToNeedleId(uint64(i+1)), Uint32ToOffset(uint32(0)), Size(1))
-		if rand.Float32() < 0.2 {
+		if rand.Float32() < 0.2 && i > 0 {
 			nm.Delete(Uint64ToNeedleId(uint64(rand.Int63n(int64(i))+1)), Uint32ToOffset(uint32(0)))
 		}
 	}