Fix a Field.isAnnotationPresent crash.

For instances of Proxy, generated at runtime, there is no corresponding
.dex file.

Bug: https://code.google.com/p/android/issues/detail?id=24846
Change-Id: I36da43d5279a61b8cb71cdf2bbc3065b6a979830
Merge "Fix a Field.isAnnotationPresent crash." into jb42