fix: handle empty time entries and add missing mypy override for openpyxl

- Treat empty list from fetch_issues_with_spent_time as 'no entries' and exit 0
  instead of crashing later in the pipeline.
- Update CLI output-extension tests to use non-empty mock data so they actually
  reach the extension validation code path.
- Add openpyxl to mypy ignore_missing_imports overrides.

Closes #36

tests/test_cli.py

@@ -71,11 +71,23 @@ def test_cli_invalid_date_format():
     assert code == 1
 
 
+class _MockIssue:
+    """Простой mock Redmine Issue для CLI-тестов."""
+
+    def __init__(self, issue_id=1, subject="Task", project="Project", status="New"):
+        self.id = issue_id
+        self.subject = subject
+        self.project = project
+        self.status = status
+        self.fixed_version = None
+
+
 @mock.patch.dict(os.environ, VALID_ENV, clear=True)
 @mock.patch("redmine_reporter.cli.fetch_issues_with_spent_time")
 def test_cli_unknown_output_extension(mock_fetch, tmp_path):
     """Неизвестное расширение файла -- выход 1."""
-    mock_fetch.return_value = []
+    issue = _MockIssue()
+    mock_fetch.return_value = [(issue, 1.0)]
     output = str(tmp_path / "report.xyz")
     code = main(["--date", "2026-01-01--2026-01-31", "--output", output])
     assert code == 1
@@ -85,7 +97,8 @@ def test_cli_unknown_output_extension(mock_fetch, tmp_path):
 @mock.patch("redmine_reporter.cli.fetch_issues_with_spent_time")
 def test_cli_output_without_extension(mock_fetch, tmp_path):
     """Файл без расширения -- выход 1 с подсказкой."""
-    mock_fetch.return_value = []
+    issue = _MockIssue()
+    mock_fetch.return_value = [(issue, 1.0)]
     output = str(tmp_path / "report")
     code = main(["--date", "2026-01-01--2026-01-31", "--output", output])
     assert code == 1
@@ -96,7 +109,8 @@ def test_cli_output_without_extension(mock_fetch, tmp_path):
 @mock.patch("redmine_reporter.cli.get_formatter_by_extension")
 def test_cli_odt_missing_odfpy_message(mock_gf, mock_fetch, tmp_path, capsys):
     """При запросе .odt без odfpy — выход 1, понятное сообщение про odfpy."""
-    mock_fetch.return_value = []
+    issue = _MockIssue()
+    mock_fetch.return_value = [(issue, 1.0)]
     mock_gf.return_value = None
     output = str(tmp_path / "report.odt")
     code = main(["--date", "2026-01-01--2026-01-31", "--output", output])