fix(firefox): guard undefined pageError.location in dispatcher

[dimirey]

What / why

A page emitting an uncaught JS error whose location is undefined crashes the entire Node driver process with an unhandled TypeError: Cannot read properties of undefined (reading 'url'), rather than surfacing the error to the client. Because the crash happens upstream of event dispatch, page.on('pageerror') cannot intercept it. Regression from #39767 (shipped 1.60.0).

Fixes #41628.

The fix

BrowserContextDispatcher's PageError listener dereferenced pageError.location.url unconditionally. Firefox can deliver an uncaught error with no location (reproducible with Firefox builds that omit it, e.g. Camoufox), so guard the access:

location: {
  url: pageError.location?.url ?? '',
  line: pageError.location?.lineNumber ?? 0,
  column: pageError.location?.columnNumber ?? 0,
},

A driver-process crash on absent protocol data is never desirable regardless of the Firefox build.

Notes

• Minimal, defensive one-liner; no behavior change when location is present.
• Happy to add a regression test if you can point me at the right fixture/harness — the trigger is a locationless uncaught page error, which needs a crafted Firefox fixture to reproduce deterministically.