Fix bug when downloading non-local files from a wiki

Revert to the pre-v0.6.0 method of checking for file existence.
A change introduced in v0.6.0 caused the check to fail if the file
existed only in a shared repository and not locally on the requested
wiki.

src/wikiget/dl.py

@@ -184,7 +184,7 @@ def download(f: File, args: Namespace) -> int:
     # prepend the current filename to all log messages
     adapter = FileLogAdapter(logger, {"filename": filename})
 
-    if file.exists:
+    if file.imageinfo:
         # file exists either locally or at a common repository, like Wikimedia Commons
         file_url = file.imageinfo["url"]
         file_size = file.imageinfo["size"]

tests/test_dl.py

@@ -307,7 +307,6 @@ def mock_file(self) -> File:
         """
         file = File(name="Example.jpg")
         file.image = Mock()
-        file.image.exists = True
         file.image.imageinfo = {
             "url": "https://upload.wikimedia.org/wikipedia/commons/a/a9/Example.jpg",
             "size": 9022,
@@ -475,7 +474,7 @@ def test_download_nonexistent_file(
         self, mock_file: File, caplog: pytest.LogCaptureFixture
     ) -> None:
         """Test that a warning message is logged if no file info was returned."""
-        mock_file.image.exists = False
+        mock_file.image.imageinfo = {}
 
         args = parse_args(["File:Example.jpg"])
         errors = download(mock_file, args)