Fix inclusion of spurious views from other projects in FollowResponse (#3116)

A logic error in https://github.com/zed-industries/zed/pull/2993 caused
follow responses to sometimes contain extra views for other unshared
projects 😱 . These views would generally fail to deserialize on the
other end. This would create a broken intermediate state, where the
following relationship was registered on the server (and on the leader's
client), but the follower didn't have the state necessary for following
into certain views.

Release Notes:

- Fixed a bug where following would sometimes fail if the leader had
another unshared project open.

crates/workspace/src/workspace.rs

@@ -2878,8 +2878,7 @@ impl Workspace {
                         let cx = &cx;
                         move |item| {
                             let item = item.to_followable_item_handle(cx)?;
-                            if project_id.is_some()
-                                && project_id != follower_project_id
+                            if (project_id.is_none() || project_id != follower_project_id)
                                 && item.is_project_item(cx)
                             {
                                 return None;