Android: Made sure we get the initial route from the intent.

[gaaclarke]

fixes b/271100292

Edit: Fixes flutter/flutter#121244.

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[gaaclarke]

attn @math1man

[camsim99]

Oh I fixed this issue here but I did something different I think because I thought the cause was different: #40119. Does this fix it? There's a repro here flutter/flutter#121244

[math1man]

This LGTM. I think this is a more consistent and efficient fix than #40119

[gaaclarke]

This fix was based off of the debugging that @math1man did. His analysis makes sense to me although @camsim99 will probably have a better sense than me about the different flows through this code.

Assuming that this works, this fix seems preferable. @math1man made a good point that there are some temporal dependencies about when you an access the activity so making sure our scenario apps pass on ci will be important. It would be nice if he could test the fix in his app just to make sure.

[math1man]

I've verified this fix locally in my app and confirmed it resolves the issue.

I would say that my biggest reason to prefer this over #40119 is that it is closer to what the behavior was before #38367 introduced this regression.

[camsim99]

cc @reidbaker

[camsim99]

Lgtm!