Check that apex#filesInfo is not nil in mixed bazel/soong mode.

filesInfo should not be used for an apex that's converted to Bazel,
since all information should come from the Bazel starlark provider.
filesInfo is populated when there's a full Android.bp module graph of
the apex deps.

Test: presubmits
Change-Id: I4b9c596ca7841f4ea76e21f929039282113b6752