refactor: remove dead code in cli and xlsx

cli.py: drop redundant 'if issue_hours is None' branch before
'if not issue_hours'. The branch is not formally dead (client
returns None when no time entries found, client.py), but it is a
semantic duplicate: both branches print the same message and
return 0, and None is falsy, so a single 'not issue_hours' check
covers None, empty list and keeps behavior identical.
test_cli_returns_zero_on_no_entries stays green unchanged.

xlsx.py: drop unreachable 'if ws is None' fallback. Workbook()
(write_only=False) always creates one worksheet in __init__, so
wb.active is never None; set the title directly.

Closes #63

redmine_reporter/formatters/xlsx.py

@@ -39,10 +39,7 @@ class XLSXFormatter(Formatter):
     def format(self, rows: List[ReportRow]) -> Workbook:
         wb = Workbook()
         ws = wb.active
-        if ws is None:
-            ws = wb.create_sheet("Report")
-        else:
-            ws.title = "Report"
+        ws.title = "Report"
 
         headers = [
             "Project",