Bugfix #2507, #2508

[nebojsact]

List of changes

• Added check for already existing active pool [Bug #2507] 🐛 PDF Backend Allows Creation of Multiple Active Poll govtool#2507
• Fixed Unable to vote after opening new voting pool [Bug #2508] 🐛 Unable to Vote on New Poll After Previous Poll is Closed govtool#2508

Checklist

• [Bug #2508] 🐛 Unable to Vote on New Poll After Previous Poll is Closed govtool#2508
• [Bug #2507] 🐛 PDF Backend Allows Creation of Multiple Active Poll govtool#2507
• My changes generate no new warnings
• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the changelog
• I have added tests that prove my fix is effective or that my feature works

[github-actions]

✅ All checks succeeded

[github-actions]

@nebojsact
This PR is in the tag: dev-d1edf6fd30f2f3474cf27a66c6ca3a5e9bf307b8 , for backend service