Set empty string as fallback for undefined version

[momesgin]

Summary

Fixes #11289

Occurred changes and/or fixed issues

I was not able to reproduce the issue, Jetstack probably has fixed their undefined version, or another change in our code has fixed it, but to be safe I've added a fallback to make sure the app doesn't break anymore.

Technical notes summary

isPrerelease gets called when user has enabled "Include Prerelease Versions" option from Preferences page. An empty string as a fallback will prevent semver.clean to throw error as it expects to receive a string, as a result isPrerelease will return false. This eventually results in not showing the problematic app on the charts page.

Areas or cases that should be tested

The repro steps doesn't work anymore. I think we can move on without testing this considering how small and safe the change is, and the undefined case being tested already in dev mode.

Areas which could experience regressions

Try enable/disable "Include Prerelease Versions" option from Preferences page, the functionality of the charts page should be the same as before.

Screenshot/Video

Checklist

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[richard-cox]

Slightly odd things happen when the user tries to install a chart with no version (the details page renders nothing and titles with (), the install option is shown).

However it's pretty borked that a chart has no version and even more so that it breaks the ui. Lets get this one in