Regression in enum default value handling in 4.7.0

[pimeys]

Bug description

In a case where we cannot decipher any name for the enum variant, in 4.7.0 a default value using this variant is rendered wrong.

In version 4.6.0 we did:

model A {
  id  Int @id
  val B @default(dbgenerated("0"))
}

enum B {
  // 0 @map("0")
}

And in version 4.7.0 we do:

model A {
  id  Int @id
  val B @default()
}

enum B {
  // 0 @map("0")
}

Both data models are invalid, but the old version had less things to fix.

git bisect shows the PR in culprit: prisma/prisma-engines#3381