stagefright: properly handle crypto object reset

Bug: 36449774
Test: Run PoC in the bug
Test: adb shell am instrument -e size small -w 'android.media.cts/android.support.test.runner.AndroidJUnitRunner'
Test: Play an encrypted content on Play Movies
Change-Id: Ia7b38ed586460ad51fa66a6959211a7dfffa3493