fix: three bugs from second code review

[daimpad]

Summary

Three bugs found and fixed by a second full-codebase review.

state.js — corrupt localStorage crashes the app

loadLocalPlayers / loadLocalMatches called JSON.parse without a try/catch. A truncated or corrupt entry (e.g. from a storage-quota mid-write) would throw a SyntaxError that propagated into the caller's catch block, which showed a misleading "Netzwerkfehler" and skipped the remote fetch entirely — leaving the app permanently stuck with no data. Fixed: wrap in try/catch, remove the corrupt entry, return false so the remote fetch proceeds normally.

chart.js — stale Chart.js instance on empty → data transition

renderEloChart returned early when there were no active players, but did not call chartInstance.destroy() first. On the next call with data, destroy() ran — but Chart.js had never formally released the canvas during the empty-state path, causing a "Canvas is already in use" warning and potentially a blank chart. Fixed: destroy the instance before the early return.

app.js — dead variable in removeMatch

const match = state.matches.find(...) was left over from the targeted-write optimisation that was reverted in PR #25. The variable was assigned but never read. Removed.

Test plan

• 56 unit tests pass (npm test)
• Manually corrupt localStorage.eloPlayers in DevTools → reload → app loads from server normally instead of crashing
• Delete all matches → switch chart type → add a match → chart renders correctly (no "Canvas already in use" warning)

https://claude.ai/code/session_01TgxiTLy7fCh5xZPJT8eTVt

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