Ensure tmp files are deleted

This doesn't seem to fix the case where an exception bubbles up to the top of
the event loop. It also doesn't seem to fix the case when a KeyboardInterrupt is
thrown, since that never makes its way into the event loop in the first place.

Both of these cases lead to the event loop stopping, which means that the tmp
file cleanup doesn't get executed even though it's inside a "with" or "finally".

PFERD/output_dir.py

@@ -3,13 +3,14 @@ import os
 import random
 import shutil
 import string
-from contextlib import asynccontextmanager
+from contextlib import asynccontextmanager, contextmanager
 from dataclasses import dataclass
 from datetime import datetime
 from enum import Enum
 from pathlib import Path, PurePath
 # TODO In Python 3.9 and above, AsyncContextManager is deprecated
-from typing import AsyncContextManager, AsyncIterator, BinaryIO, Optional
+from typing import (AsyncContextManager, AsyncIterator, BinaryIO, Iterator,
+                    Optional)
 
 from rich.markup import escape
 
@@ -327,23 +328,29 @@ class OutputDirectory:
             mtimestamp = mtime.timestamp()
             os.utime(info.local_path, times=(mtimestamp, mtimestamp))
 
+    @contextmanager
+    def _ensure_deleted(self, path: Path) -> Iterator[None]:
+        try:
+            yield
+        finally:
+            path.unlink(missing_ok=True)
+
     async def _after_download(self, info: DownloadInfo) -> None:
+        with self._ensure_deleted(info.tmp_path):
             changed = False
 
             if not info.success:
-            info.tmp_path.unlink()
                 return
 
             # Solve conflicts arising from existing local file
             if info.local_path.exists():
                 changed = True
+
                 if filecmp.cmp(info.local_path, info.tmp_path):
                     self._update_metadata(info)
-                info.tmp_path.unlink()
                     return
 
                 if not await self._conflict_lfrf(info.on_conflict, info.path):
-                info.tmp_path.unlink()
                     return
 
             info.tmp_path.replace(info.local_path)