Fix nil pointer panic in deposits page

[barnabasbusa]

Fixing:

URL: /validators/deposits?v=transactions
  Time: 2026-03-11 11:38:32.422113953 +0000 UTC m=+941.757111511
  Version: git-2f8fe15

  Error:
  page call 59 panic: runtime error: invalid memory address or nil pointer dereference

  Stack Trace:
  goroutine 4846 [running]:
  runtime/debug.Stack()
      /opt/hostedtoolcache/go/1.25.8/arm64/src/runtime/debug/stack.go:26 +0x64
  github.com/ethpandaops/dora/services.(*FrontendCacheService).processPageCall.func1.1()
      /home/runner/work/dora/dora/services/frontendcache.go:166 +0x90
  panic({0x20b15c0?, 0x5a62ac0?})
      /opt/hostedtoolcache/go/1.25.8/arm64/src/runtime/panic.go:783 +0x120
  github.com/ethpandaops/dora/handlers.buildDepositsPageData({0x46c6da0, 0x400277a0f0}, 0xffffffffffffffff?, 0x32, {0x4002af73fb, 0xc})
      /home/runner/work/dora/dora/handlers/deposits.go:185 +0x7f0
  github.com/ethpandaops/dora/handlers.getDepositsPageData.func1(0x4003195f20)
      /home/runner/work/dora/dora/handlers/deposits.go:73 +0x2c
  github.com/ethpandaops/dora/services.(*FrontendCacheService).processPageCall.func1(0x4002ae4600?)
      /home/runner/work/dora/dora/services/frontendcache.go:211 +0x2a4
  created by github.com/ethpandaops/dora/services.(*FrontendCacheService).processPageCall in goroutine 4656
      /home/runner/work/dora/dora/services/frontendcache.go:160 +0x2dc

Summary

• GetValidatorByIndex can return nil even when the validator index is known (e.g. during sync), but all three call sites in buildDepositsPageData dereferenced it without a nil check, causing a panic on /validators/deposits?v=transactions
• Added nil guard to all three locations, falling back to "Deposited" status (consistent with the existing fallback when the validator index isn't found)

Test plan

• Visit /validators/deposits?v=transactions during initial sync when validator state may be incomplete
• Verify no panic occurs and deposits show "Deposited" status for validators not yet loaded

🤖 Generated with Claude Code