[go_router] Fix Android Cold Start deep link with empty path losing scheme and authority.

[nozomemein]

Description

Fixes an issue where deep links with empty paths (e.g., https://example.com) lose their scheme and authority information during Android Cold Start.

This PR fixes flutter/flutter#174249

Detailed reproduction steps, environment information, and code sample are provided in the linked issue.

Problem

On Android Cold Start, if the initial deep link has no path (https://example.com),
_effectiveInitialLocation incorrectly creates a new Uri with only /? instead of preserving scheme and authority.
This results in the router receiving a relative path instead of the full deep link URL.

Solution

Use Uri.replace(path: '/') instead of creating a new Uri, so that the original scheme and authority are preserved.

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[chunhtai]

LGTM

[chunhtai]

I think this todo is obsolete now, can you remove this todo?

[nozomemein]

deleted in the commit below!

• 84da17c