[camera_android_camerax] Fix setFocusMode(auto) crash when there is no auto-focus point

[motucraft]

Adds the missing isEmpty guard to the FocusMode.auto branch of AndroidCameraCameraX.setFocusMode, which read meteringPointsAf.first unconditionally and threw StateError: Bad state: No element when the current focus-and-metering action had no auto-focus point.

The FocusMode.locked branch already guards this; the auto branch did not.

Fixes flutter/flutter#187782

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Code Review

This pull request fixes a StateError in setFocusMode(FocusMode.auto) when the current focus and metering action has no auto-focus points. The implementation safely retrieves the list of auto-focus points and checks if it is empty before accessing the first element. A unit test has been added to verify this behavior, and the package version has been bumped to 0.7.2+2. There are no review comments to address.

[camsim99]

LGTM! Thank you for the extremely well-written bug and a straightforward fix :)

[reidbaker]

This does not make sense to me. let me rewrite the turnary to an if statement to make it a bit easier to read.

if(_defaultFocusPointLocked || possibleCurrentAfPoints.isEmpty) {
   return null
} else {
   return possibleCurrentAfPoints.first;
}

I believe this code will throw a state error if _defaultFocusPointLocked == true and possibleCurrentAfPoints is an empty list. Which looks like the error you are claiming to fix.

Did I make a mistake or is there something I am misunderstanding?

[motucraft]

@reidbaker

Thanks for the review. I think this should not throw. With this condition, possibleCurrentAfPoints.first is only evaluated when _defaultFocusPointLocked is false and possibleCurrentAfPoints is not empty. If _defaultFocusPointLocked is true or the list is empty, the expression returns null.

Please let me know if I’m missing something.

[reidbaker]

facepalm, yes sorry reviewing code tired will do that. Thank you for responding with grace.

[motucraft]

This PR became conflicted while waiting after approval. I’ve merged the latest main and resolved the conflicts.