add newline to last line of portfolio_to_csv output (#158)

* add newline to last line of portfolio_to_csv output

* Update pytr/portfolio.py

* ruff format

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Co-authored-by: Niklas Rosenstein <rosensteinniklas@gmail.com>

Author: marcusfey

pytr/portfolio.py

@@ -89,7 +89,7 @@ def portfolio_to_csv(self, output_path):
 
         with open(output_path, "w", encoding="utf-8") as f:
             f.write("Name;ISIN;quantity;avgCost;netValue\n")
-            f.write("\n".join(csv_lines))
+            f.write("\n".join(csv_lines) + ("\n" if csv_lines else ""))
 
         print(f"Wrote {len(csv_lines) + 1} lines to {output_path}")