`place_photos_uri` / `place_photos_image` reject `&str`/`String` inputs (missing `From<Infallible> for Error`)

[joeblew999]

The documented "pass a photo resource name" usage doesn't compile on master (v3.9.6):

let client = google_maps::Client::new(key);
let _ = client.place_photos_uri("places/XXX/photos/YYY"); // a Place.photos[].name value

error[E0277]: the trait bound `GoogleMapsError: From<Infallible>` is not satisfied
   --> src/.../uri/request.rs
    = note: required for `Infallible` to implement `Into<GoogleMapsError>`
note: required by a bound in `place_photos_uri`
    |  P::Error: Into<crate::Error>,

Cause: both place_photos_uri and place_photos_image are bounded
where P: TryInto<PhotoRequest>, P::Error: Into<crate::Error>. For the From-based conversions
(&str / String / PhotoRequest → PhotoRequest) the TryInto::Error is
std::convert::Infallible, and Error: From<Infallible> isn't implemented — so the bound is
unsatisfiable. In practice these methods are only reachable via TryFrom<&Place>, not with the
photo resource-name string the API actually hands you in Place.photos[].name.

Fix: add a total, zero-cost conversion (Infallible is uninhabited):

impl std::convert::From<std::convert::Infallible> for Error {
    fn from(value: std::convert::Infallible) -> Self { match value {} }
}

This makes the string-input call sites work and is purely additive. Happy to send a PR.