When the drawer is open and gets disposed during locked framework it still removes its controller history entry in dispose, leading to a setState response in Scaffold to close the drawer. This led to an exception and a broken BackButton in the AppBar in certain situations.

This PR adds a check before the drawer and endDrawer opened callback setState to ensure that the drawer state still exists to avoid the issue. I considered adding it to a post-frame callback but it runs into the issue of the scaffold being disposed along with the drawer and then triggering setState for a disposed state.

Fixes #34978

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the Flutter Style Guide, including Features we expect every widget to implement.
• I signed the CLA.
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• All existing and new tests are passing.