Fix style image methods hang&exception

[evil159]

What does this pull request do?

Fixes hasStyleImage hanging and getStyleImage causing exception from Flutter's method channel on Android.

What is the motivation and context behind this change?

Pull request checklist:

• [ ] Add a changelog entry.
• [ ] Write tests for all new functionality. If tests were not written, please explain why.
• [ ] Add documentation comments for any added or updated public APIs.