Don't crash the app when the assist structure cannot be retrieve.

When an app trigger autofill, system_server will eventually call back into the
app to lazy load the contents of the AssistStructure used for autofill. If that
binder transaction fails, we should simple ignore it, rather than crash the app.

Test: atest CtsAutoFillServiceTestCases
Test: locally changed code to force WTFs and called 'adb shell dumpsys autofill'

Bug: 72398988

Change-Id: I490ad877b067fb37997b734718b90b00f9d318c8