Handle path generation error for #switch

What does this MR do and why?

Contributes to #386836 (closed)

Problem

A specially crafted path value can lead to UrlGeneration error.

Solution

Handle UrlGeneration error and return 400 error instead.

MR acceptance checklist

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Screenshots or screen recordings

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Before	After

How to set up and validate locally

1. Visit http://127.0.0.1:3000/gitlab-org/gitlab-shell/-/refs/switch?ref=main&ref_type=heads&path=*&destination=graphs
2. You should see a Bad Request error instead of Internal Server.