Patch visualizer doesn't display failed instance additions

[kennethloeffler]

While reproducing the issue described in #841, I noticed some odd behavior from the patch visualizer. To reproduce, download the following project and follow the steps below: part-package.zip. This reproduces on Rojo 7.4.0.

1. Run rojo serve on the provided project.
2. Open a fresh baseplate in Roblox Studio and connect the Rojo plugin. With trace output enabled, you should see something like this after accepting the initial sync:
   

PackageLink is not creatable. The trace output shows that the PackageLink addition is being added to the unapplied patch, and the status indicator correctly reports that 5 changes (4 properties on the part plus the failed PackageLink addition) failed to apply, but the expanded patch visualizer does not indicate the failure.

cc @boatbomber