Use bool::then instead of then_some with function calls (#6156)

I noticed that hardware benchmarks are being run even though we pass the
--no-hardware-benchmarks cli flag. After some debugging, the cause is an
incorrect usage of the `then_some` method.

From [std
docs](https://doc.rust-lang.org/std/primitive.bool.html#method.then_some):

> Arguments passed to then_some are eagerly evaluated; if you are
passing the result of a function call, it is recommended to use
[then](https://doc.rust-lang.org/std/primitive.bool.html#method.then),
which is lazily evaluated.

```rust
let mut a = 0;
let mut function_with_side_effects = || { a += 1; };

true.then_some(function_with_side_effects());
false.then_some(function_with_side_effects());

// `a` is incremented twice because the value passed to `then_some` is
// evaluated eagerly.
assert_eq!(a, 2);
```

This PR fixes all the similar usages of the `then_some` method across
the codebase.

polkadot address: 138eUqXvUYT3o4GdbnWQfGRzM8yDWh5Q2eFrFULL7RAXzdWD

---------

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>
Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>