Fix issue #1802: Handle UnicodeDecodeError in repo file paths

Added error handling for UnicodeDecodeError when decoding paths in the Git repository.
This issue arises when paths are encoded in formats other than the expected system encoding.

The error handler now provides a detailed error message, helping users identify potential encoding mismatches.

Closes #1802

tests/basic/test_sanity_check_repo.py

@@ -8,6 +8,8 @@ from git import GitError, Repo
 
 from aider import urls
 from aider.main import sanity_check_repo
+from aider.repo import GitRepo
+from aider.io import InputOutput
 
 
 @pytest.fixture
@@ -182,3 +184,41 @@ def test_sanity_check_repo_with_no_repo(mock_io):
     # Assert that no errors or outputs were logged
     mock_io.tool_error.assert_not_called()
     mock_io.tool_output.assert_not_called()
+
+
+def corrupt_git_index(repo_path):
+    index_path = os.path.join(repo_path, ".git", "index")
+    with open(index_path, "r+b") as f:
+        # Verify the file has the correct signature
+        signature = f.read(4)
+        if signature != b"DIRC":
+            raise ValueError("Invalid git index file signature.")
+
+        # Seek to the data section and inject invalid bytes to simulate encoding error
+        f.seek(77)
+        f.write(b"\xF5" * 5)
+
+
+def test_sanity_check_repo_with_corrupt_index(create_repo, mock_io):
+    repo_path, repo = create_repo
+    # Corrupt the Git index file
+    corrupt_git_index(repo_path)
+
+    # Create GitRepo instance
+    git_repo = GitRepo(InputOutput(), None, repo_path)
+
+    # Call the function
+    result = sanity_check_repo(git_repo, mock_io)
+
+    # Assert that the function returns False
+    assert result is False
+
+    # Assert that the appropriate error messages were logged
+    mock_io.tool_error.assert_called_with("Unable to read git repository, it may be corrupt?")
+    mock_io.tool_output.assert_called_with(
+        (
+            "Failed to read the Git repository. This issue is likely caused by a path encoded "
+            "in a format different from the expected encoding \"utf-8\".\n"
+            "Internal error: 'utf-8' codec can't decode byte 0xf5 in position 3: invalid start byte"
+        )
+    )