Remove subaggregator check from CompositeAggregator

Not sure why I added this, when the existing implementation didn't have it.

That said, we *should* call finishLeaf() before precomputing the current leaf.

Signed-off-by: Michael Froh <froh@amazon.com>

server/src/main/java/org/opensearch/search/aggregations/bucket/composite/CompositeAggregator.java

@@ -557,10 +557,8 @@ private void processLeafFromQuery(LeafReaderContext ctx, Sort indexSortPrefix) t
 
     @Override
     protected boolean tryPrecomputeAggregationForLeaf(LeafReaderContext ctx) throws IOException {
-        if (subAggregators().length == 0) {
-            return filterRewriteOptimizationContext.tryOptimize(ctx, this::incrementBucketDocCount, segmentMatchAll(context, ctx));
-        }
-        return false;
+        finishLeaf(); // May need to wrap up previous leaf if it could not be precomputed
+        return filterRewriteOptimizationContext.tryOptimize(ctx, this::incrementBucketDocCount, segmentMatchAll(context, ctx));
     }
 
     @Override