add crash test case.
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FATAL EXCEPTION: Thread-4115
java.lang.NullPointerException: key == null || value == null
at android.support.v4.util.LruCache.put(LruCache.java:117)
at com.diegocarloslima.byakugallery.lib.TileBitmapDrawable$DecoderWorker.run(TileBitmapDrawable.java:453)
fix crash bug on black rectangle.