Fix exception in navigation observer with Flutter 3.35.3

[BDR-Thermea-B2B-apps]

Description of the change

Hello,

It looks like when popping back to the root of our app the Instabug navigation observer causes an uncaught exception when removing an item from a list that is empty. There is an if check around it but it is an async/await. So it looks like in the meantime while the async call is running the list can change, causing this exception.

So I suspect it goes like this

if _steps.isNotEmpty -> reportScreenChange gets called and asynchronously _steps gets changed -> _steps.removeLast(); on a now empty list without checking if it is empty after the await

https://github.com/Instabug/Instabug-Flutter/issues/640

E/flutter ( 6807): [ERROR:flutter/runtime/dart_vm_initializer.cc(40)] Unhandled Exception: RangeError (length): Invalid value: Valid value range is empty: -1
E/flutter ( 6807): #0      List.[] (dart:core-patch/growable_array.dart)
E/flutter ( 6807): #1      List.removeLast (dart:core-patch/growable_array.dart:345:20)
E/flutter ( 6807): #2      InstabugNavigatorObserver.screenChanged.<anonymous closure> (package:instabug_flutter/src/utils/instabug_navigator_observer.dart:33:18)
E/flutter ( 6807): <asynchronous suspension>

Type of change

• [x] Bug fix (non-breaking change that fixes an issue)
• [ ] New feature (non-breaking change that adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Related issues

Issue links go here

Checklists

Development

• [x] Lint rules pass locally
• [x] The code changed/added as part of this pull request has been covered with tests

Code review

• [ ] This pull request has a descriptive title and information useful to a reviewer
• [ ] Issue from task tracker has a link to this pull request