fix(gitea): don't crash on empty body during pagination

[CirnoT]

Fixes #6600

         {
           "name": "renovate",
           "level": 50,
           "logContext": "KVZYKAwSe",
           "repository": "***",
           "err": {
             "message": "pc.push is not iterable (cannot read property Symbol(Symbol.iterator))",
             "stack": "TypeError: pc.push is not iterable (cannot read property Symbol(Symbol.iterator))\n    at GiteaHttp.request (/usr/src/app/node_modules/renovate/dist/util/http/gitea.js:46:20)\n    at runMicrotasks (<anonymous>)\n    at processTicksAndRejections (internal/process/task_queues.js:97:5)\n    at async GiteaHttp.requestJson (/usr/src/app/node_modules/renovate/dist/util/http/index.js:135:21)\n    at async Object.searchIssues (/usr/src/app/node_modules/renovate/dist/platform/gitea/gitea-helper.js:145:17)\n    at async Proxy.ensureIssueClosing (/usr/src/app/node_modules/renovate/dist/platform/gitea/index.js:553:27)\n    at async Object.exports.isOnboarded (/usr/src/app/node_modules/renovate/dist/workers/repository/onboarding/branch/check.js:51:9)\n    at async Object.checkOnboardingBranch (/usr/src/app/node_modules/renovate/dist/workers/repository/onboarding/branch/index.js:14:29)\n    at async Object.initRepo (/usr/src/app/node_modules/renovate/dist/workers/repository/init/index.js:44:14)\n    at async Object.renovateRepository (/usr/src/app/node_modules/renovate/dist/workers/repository/index.js:37:18)\n    at async Object.start (/usr/src/app/node_modules/renovate/dist/workers/global/index.js:76:13)\n    at async /usr/src/app/node_modules/renovate/dist/renovate.js:28:24"
           },
           "msg": "Repository has unknown error"
         }

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[renovate-release]

🎉 This PR is included in version 21.18.7 🎉

The release is available on:

• GitHub release
• 21.18.7

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