Summary:
Fixed clang static analyzer warning about division by 0.
```
ar: creating librocksdb_debug.a
tools/db_bench_tool.cc:4650:43: warning: Division by zero
int pos = static_cast<int>(rand_num % range_);
~~~~~~~~~^~~~~~~~
1 warning generated.
make: *** [analyze] Error 1
```
This is from the new code I recently merged in ce8e88d2d7a62e2a08c4109aac84cb9e95ed359b.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4910
Differential Revision: D13788037
Pulled By: sagar0
fbshipit-source-id: f48851dca85047c19fbb1a361e25ce643aa4c7ea
0cead31d10