fix(firebase_ui_database): Perform list operations in correct order

[Rexios80]

Description

Fix for bug introduced by #193

The elements should be reversed before removing the extra element or else the wrong element is removed

Related Issues

N/A

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[Rexios80]

@rrousselGit @lesnitsky Can we get this merged? This is a pretty important issue that affects the currently released package.

[russellwheatley]

Hey @Rexios80 - sorry for the late response, I had this on my radar but I wanted to write firebase_ui_database tests. They have just been merged, is it possible that you could write a test that validates the change? At the moment, our CI is broken on apple CI due to an external dependency that we're in the process of fixing. It will work locally. Here are the tests: https://github.com/firebase/FirebaseUI-Flutter/blob/main/tests/integration_test/firebase_ui_database/database_list_view_test.dart

You will need to run firebase emulators:start in root of project and run flutter test integration_test/firebase_ui_test.dart. Also worth commeting out tests you don't need to run for speed here: https://github.com/firebase/FirebaseUI-Flutter/blob/main/tests/integration_test/firebase_ui_test.dart#L26-L36

Thanks 👍

[Rexios80]

@russellwheatley I wrote the test

[russellwheatley]

@Rexios80 - thanks, I will look to get this merged/released this week 👍