LUCENE-10311: avoid division by zero on small sets.
diff --git a/lucene/core/src/java/org/apache/lucene/util/FixedBitSet.java b/lucene/core/src/java/org/apache/lucene/util/FixedBitSet.java
index ec1b676..5566bd0 100644
--- a/lucene/core/src/java/org/apache/lucene/util/FixedBitSet.java
+++ b/lucene/core/src/java/org/apache/lucene/util/FixedBitSet.java
@@ -204,7 +204,7 @@
     final int rangeLength = 16;
     final int interval = 1024;
 
-    if (numWords < interval) {
+    if (numWords <= interval) {
       return cardinality();
     }