Search doesn't handle Slots without Blocks

[catch-21]

Summary

When a search is performed for a slot number where no block exists then nothing happens and the search field breaks, requires page refresh.

Steps to reproduce

1. Navigate to https://explorer.alonzo-purple.dev.cardano.org
2. Type 361 into search field
3. Click on "Search for a block by slot"

Actual Result

Still at homepage. No result shown. Search field is now broken (doesn't show suggestion dropdown when changing input)

Desired result

Some feedback to say this block doesn't exist