options_util_test fails if vector size is 0

### Expected behavior
options_util_test to succeed every time.

### Actual behavior

utilities/options/options_util_test.cc:62: Failure
PersistRocksDBOptions(db_opt, cf_names, cf_opts, kFileName, env_->GetFileSystem().get())
Invalid argument: [RocksDBOptionsParser]: failed the verification on ColumnFamilyOptions::max_bytes_for_level_multiplier_additional--- The specified one is while the persisted one is 1:1:1:1:1:1:1.

### Steps to reproduce the behavior

My machine is regularly creating a "random" column family with zero as the number of levels. This leads to the max_bytes_for_level_multiplier_additional vector to be of size zero. Looks like the code reading the "persisted" is leaving the vector in an default state instead of clearing it.

forcing the number of levels to size 1 or larger fixed the problem.