ffi: Use the SDK's (tested) logic for overriding the sliding sync proxy.

bindings/matrix-sdk-ffi/src/client_builder.rs

@@ -527,6 +527,10 @@ impl ClientBuilder {
 
         inner_builder = inner_builder.with_encryption_settings(builder.encryption_settings);
 
+        if let Some(sliding_sync_proxy) = builder.sliding_sync_proxy {
+            inner_builder = inner_builder.sliding_sync_proxy(sliding_sync_proxy);
+        }
+
         inner_builder =
             inner_builder.simplified_sliding_sync(builder.is_simplified_sliding_sync_enabled);
 
@@ -536,25 +540,6 @@ impl ClientBuilder {
 
         let sdk_client = inner_builder.build().await?;
 
-        // At this point, `sdk_client` might contain a `sliding_sync_proxy` that has
-        // been configured by the homeserver (if it's a `ServerName` and the
-        // `.well-known` file is filled as expected).
-        //
-        // If `builder.sliding_sync_proxy` contains `Some(_)`, it means one wants to
-        // overwrite this value. It would be an error to call
-        // `sdk_client.set_sliding_sync_proxy()` with `None`, as it would erase the
-        // `sliding_sync_proxy` if any, and it's not the intended behavior.
-        //
-        // So let's call `sdk_client.set_sliding_sync_proxy()` if and only if there is
-        // `Some(_)` value in `builder.sliding_sync_proxy`. That's really important: It
-        // might not break an existing app session, but it is likely to break a new
-        // session, which not immediate to detect if there is no test.
-        if !builder.is_simplified_sliding_sync_enabled {
-            if let Some(sliding_sync_proxy) = builder.sliding_sync_proxy {
-                sdk_client.set_sliding_sync_proxy(Some(Url::parse(&sliding_sync_proxy)?));
-            }
-        }
-
         Ok(Arc::new(
             Client::new(
                 sdk_client,