Don't panic on From i32

[rusty-snake]

Previous discussed in #41 but closed w/o result.

https://doc.rust-lang.org/std/convert/trait.From.html says:

Note: This trait must not fail. The From trait is intended for perfect conversions. If the conversion can fail or is not perfect, use TryFrom.

[…] the general expectation is that the conversions should typically be restricted as follows:

• The conversion is infallible: if the conversion can fail, use TryFrom instead; don’t provide a From impl that panics.