Generated CreateForm: Catch statement throws an error itself (Handle graphql errors properly)

### Problem:

onSubmit handler has a `catch` block:

`
} catch (err) {
if (onError) {
const messages = err.errors.map((e) => e.message).join("\n");
onError(modelFields, messages);
}
}
`

err does not necessarily have an `errors` attribute, which will result in an error thrown: `TypeError: Cannot read properties of undefined (reading 'map')`.

Locate the generated CreateForm onSubmit handler and inspect its catch block. Reproduce an error without an errors attribute and verify it no longer causes a secondary TypeError, while GraphQL errors still reach onError with their messages.

Written by the indexing model from the issue text.