Store: Fix panic too smaller buffer

pkg/store/bucket.go

@@ -3577,10 +3577,10 @@ func (r *bucketChunkReader) loadChunks(ctx context.Context, res []seriesEntry, a
 	bufPooled, err := r.block.chunkPool.Get(r.block.estimatedMaxChunkSize)
 	if err == nil {
 		buf = *bufPooled
+		defer r.block.chunkPool.Put(&buf)
 	} else {
 		buf = make([]byte, r.block.estimatedMaxChunkSize)
 	}
-	defer r.block.chunkPool.Put(&buf)
 
 	for i, pIdx := range pIdxs {
 		// Fast forward range reader to the next chunk start in case of sparse (for our purposes) byte range.