bug(fmt): quick-fixes break with no newline after model in schema

[Druue]

Bug description

When a schema-file has no newline after the last model, lib::offset_to_position() panics. This also then results in no quick-fixes (populated from engines) being available as they all rely on this function.

running 1 test
thread 'code_actions::tests::relation_mode_prisma_missing_index' panicked at 'called `Option::unwrap()` on a `None` value', prisma-fmt/src/code_actions/relations.rs:336:79
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
test code_actions::tests::relation_mode_prisma_missing_index ... FAILED

failures:

failures:
    code_actions::tests::relation_mode_prisma_missing_index

test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 11 filtered out; finished in 0.01s

error: test failed, to rerun pass `-p prisma-fmt --test code_actions_tests`

Screen.Recording.2022-11-25.at.12.56.02.mov

Expected behavior

This should still just work

Prisma information

generator client {
    provider = "prisma-client-js"
    previewFeatures = ["referentialIntegrity"]
}

datasource db {
    provider = "mysql"
    url = env("TEST_DATABASE_URL")
    relationMode = "prisma"
}

model SomeUser {
    id Int @id
    posts Post[]
}

model Post {
    id Int @id
    userId Int
    user SomeUser @relation(fields: [userId], references: [id])
} // no newline