A segmentation fault in routing_filter_lookup

[deukyeon]

I ran into a segmentation fault in routing_filter_lookup() while running the YCSB-C benchmark.

To reproduce this problem, you could do the following steps:

1. Checkout the splinterdb's branch, [585-a-segmentation-fault-in-routing_filter_lookup](https://github.com/vmware/splinterdb/tree/585-a-segmentation-fault-in-routing_filter_lookup) and compile the code.
2. Checkout the branch called dont_merge in the YCSB-C repo (https://github.com/deukyeon/YCSB-C/tree/dont_merge) and compile.
3. Run this command ./ycsbc -db splinterdb -threads 32 -L workloads/write_intensive_10M_uniform.spec -W workloads/write_intensive_10M_uniform.spec -p splinterdb.filename /dev/nvme1n1.