Aggregation of partial entries not working

[fheft]

Aggregating time entries as described in the docs (yaml_format.md) does not work.

After displaying the list of entries, buchungsstreber exits silently.

Example:

buchungen.yml:

2025-01-22:
- 08:00-09:00 Entwicklung 50000  ExampleText
- 09:00-10:00             50000

Output after executing buchungsstreber:

BUCHUNGSSTREBER v2.11.1
~~~~~~~~~~~~~~~~~~~~~~~

  Wed:  2.0h  @  <redacted issue title>                        ExampleText         

Process finished with exit code 0

---

The issue seems to be that entries are first validated and then aggregated. As entries using the aggregation feature (- 09:00-10:00 50000) are not valid by themselves, the program terminates.
No error is displayed as the invalid entry no longer exists by then (having been aggregated with a valid entry).

See app.cli lines 30 (validation), 31 (aggregation) and 45 (exiting).