First check attempt of new pending objects is skipped, but counts

Describe the bug

Hello!

Today I tested a bit with delayed sending of notifications and was surprised to see the first check attempt of every new created pending object was invalid and skipped, but counted as such. Is this intended behaviour?

To Reproduce

1. 00:01m - 00:24m - a new object waits to be scheduled (1st attempt)
2. 00:24m - 00:57m - a 5m check_interval without a check source is executed, but suddenly skipped (this counts as 1st attempt)
3. 00:57m - 01:06m - a new check attempt with a check source is executed (2nd attempt)

Expected behavior

Only valid check attempts should be counted.

Video

https://github.com/user-attachments/assets/f6e9e08b-377e-4588-8011-a61e0a0ad269

Your Environment

Include as many relevant details about the environment you experienced the problem in

• Version used (icinga2 --version): 2.16.4
• Operating System and version: rhel 8.10
• Enabled features (icinga2 feature list): Enabled features: api checker icingadb influxdb mainlog notification
• Icinga Web 2 version and modules (System - About): 2.14.0

Start by reproducing the reported delayed-sending sequence on Icinga 2 2.16.4, focusing on the check interval that has no check source and is counted as the first attempt. Trace where pending-object attempts are validated and counted; done means invalid or skipped attempts are not included in the attempt count while valid checks still are.