fixed invalid url old timerseries

[Shrhawk]

Checklist:

• [ ] All tests are passing
• [ ] I have added any necessary documentation and/or release notes
• [ ] I have followed the commit message guidelines and the "before submitting a pull request" guidelines
• [ ] If I introduced (or abolished) any third-party library, I will write a short paragraph in this PR according to the guidelines
• [ ] I have removed all obsoleted code

[Shrhawk]

https://github.com/openmeteo/enhydris/issues/493

[Shrhawk]

Closed in favor of https://github.com/openmeteo/enhydris/pull/495 (renamed the branch)