Throw StatusCode error if http response is non-success

to prevent a misleading deserialization error on error responses.

src/api/mod.rs

@@ -243,6 +243,7 @@ impl ToTokens for Api {
                 #[allow(unused_variables)]
                 fn future_from(http_response: ::http::Response<Vec<u8>>)
                 -> Box<_Future<Item = Self, Error = Self::Error>> {
+                    if http_response.status().is_success() {
                         #extract_headers
 
                         #deserialize_response_body
@@ -255,6 +256,9 @@ impl ToTokens for Api {
                         });
 
                         Box::new(future_response)
+                    } else {
+                        Box::new(::futures::future::err(::ruma_api::Error::StatusCode(http_response.status().clone())))
+                    }
                 }
             }