Merge "stagefright: add nullptr check in MediaCodecSource" am: 11d6c4cf58 am: dd5a2f0f0b am: 050ec9ecd7

Original change: https://android-review.googlesource.com/c/platform/frameworks/av/+/1662900

Change-Id: I9d8c547ab372b4ebd4896cee6c6e61bcc8d5383b