Crash when doing an update that adds a constructor

[pchiusano]

Reported by Kyle Goetz

unique type model.ResourceType
  = Device
  | BridgeHome
  -- [snip]
  | SmartScene
  | Taurus
The only thing I’ve done is add | Taurus to the end.
When I run update:
huenison/backup> update

  Okay, I'm searching the branch for code that needs to be updated...

  That's done. Now I'm making sure everything typechecks...

Encountered exception:
Maybe.fromJust: Nothing
CallStack (from HasCallStack):
  error, called at libraries/base/Data/Maybe.hs:149:21 in base:Data.Maybe
  fromJust, called at src/Unison/Codebase/Editor/HandleInput/Update2.hs:327:52 in unison-cli-0.0.0-IVNBXmTzObr3Tub8V1XXEr:Unison.Codebase.Editor.HandleInput.Update2

[aryairani]

Yikes, unexpected. Thanks for the report.

[aryairani]

A simple case doesn't crash:

```ucm:hide
.> project.create test

unique type Foo = A | B

test/main> add

unique type Foo = A | B | C

test/main> update

[aryairani]

This case also doesn't crash, but does print an error asking you to add constructors for Bar

```ucm:hide
.> project.create test

unique type Foo = A | B

test/main> add
test/main> alias.type Foo Bar

unique type Bar = A | B | C

test/main> update

[aryairani]

This does reproduce it, though it's a long-ish download:

```ucm:hide
.> clone @kylegoetz/huenison/fromjust-bug

unique type model.ResourceId
    = ResourceId.internal (Text, Text, Text, Text, Text)

@kylegoetz/huenison/fromjust-bug> update

Note that this repro does not add a constructor, it just renames one.