Fixed heap-buffer-overflow issue when Options.num_levels > 7.

Summary:
Currently, when num_levels has been changed to > 7, internally
it will not resize max_bytes_for_level_multiplier_additional.
As a result, max_bytes_for_level_multiplier_additional.size() will
be smaller than num_levels, which causes heap-buffer-overflow.

Test Plan: make all check

Reviewers: haobo, sdong, ljin

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19275

util/options.cc

@@ -154,6 +154,9 @@ ColumnFamilyOptions::ColumnFamilyOptions(const Options& options)
       max_successive_merges(options.max_successive_merges),
       min_partial_merge_operands(options.min_partial_merge_operands) {
   assert(memtable_factory.get() != nullptr);
+  if (max_bytes_for_level_multiplier_additional.size() < num_levels) {
+    max_bytes_for_level_multiplier_additional.resize(num_levels, 1);
+  }
 }
 
 DBOptions::DBOptions()