Propagate error if retrieving encoded length fails instead of panic

[wiktor-k]

No description provided.

[wiktor-k]

I'm wondering what do you all think about the second commit that disallows using unwraps? (the only one instance was the thing fixed by the first commit).

[wiktor-k]

Okay, let's go with it for the time being...

I've also experimented with the following in Cargo.toml (courtesy of @hko-s):

[lints.clippy]
expect_used = "warn"
panic = "warn"
todo = "warn"
unimplemented = "warn"
unwrap_used = "warn"

Unfortunately (or fortunately?) it applies also to tests and examples so it's a more significant change.