Epic is displaying a splash page instead of the roadmap view
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### Summary
<!-- Summarize the bug encountered concisely. -->
### Steps to reproduce
Seems to occur only on Epics where there are no dates on child issues
View and Epic and click on the Roadmap tab:

### Example Project
- Without dates (bug) https://gitlab.com/groups/gitlab-org/-/epics/6672
- With dates (renders roadmap): https://gitlab.com/groups/gitlab-org/-/epics/4932
### What is the current *bug* behavior?
<!-- Describe what actually happens. -->
### What is the expected *correct* behavior?
- Roadmap should render a placeholder if the issues need dates. Should not show the splash page for the feature.
### Possible fixes
<!-- If you can, link to the line of code that might be responsible for the problem. -->
issue