Check for null state before adding drawable to cache

Some drawables can have a null ConstantState. Check before attempting to
add them to the cache, as the LRU does not accept null values.

Bug: N/A
Test: N/A
Change-Id: I9db20ab8f4a2e8fbbb32d9e9fc7a435482878369
(cherry picked from commit bce755f4990ad48da7b6f5079e8b0ff26c51c88c)
1 file changed