Small clean-ups (including fix for UB)

[niklasf]

Most of these are trivial. I'll highlight some important bits with inline comments.

[niklasf]

Returning 0xff here was somewhat questionable (as a bool is expected in C++ land), but not a problem as far as I can tell after reading the current implementation in RocksDB.

[niklasf]

I believe this was undefined behavior because the temporary c_int would be out of scope before the pointer is used in the called function.

Aditionally, there would be an out-of-bounds read if cfs_v.len() > 1, because the implementation expects a pointer to cfs_v.len() consecutive entries.

[stanislav-tkach]

Perhaps I'm missing something, but where can out-of-bound read occur? cfnames? But it is an array, so everything should be OK. Am I missing something?

[niklasf]

I mean the ttls array. Previously we were passing a pointer to a single integer value (&(ttl.as_secs() as c_int) as *const _), but cfs_v.len() integer values are expected (https://github.com/facebook/rocksdb/blob/f20b674796ffd7ca32471705876fc651b8e246db/db/c.cc#L827-L828), one for each column family.

[niklasf]

Oh, looks like the pointers to temporaries are fine, actually:

The drop scope of the temporary is usually the end of the enclosing statement.

https://doc.rust-lang.org/stable/reference/expressions.html?highlight=Tempo#temporaries

That leaves only the out of bounds read as UB, with all other changes being cosmetic.

[stanislav-tkach]

Perhaps I'm missing something, but where can out-of-bound read occur? cfnames? But it is an array, so everything should be OK. Am I missing something?

[niklasf]

Rebased since #627 got merged first.

[niklasf]

Prepared rustsec advisory rustsec/advisory-db#1237.

The changes in this PR are related, because they all adressed clippy lints, but I can split it, if that would be useful. The commits can also be viewed separately.