[automerger] M3UParser: handle missing EXT-X-MEDIA URIs am: b8c3a74de5 am: a3acb4c0f2 am: b7b790ef84 am: 17ae208764 am: c60f2ff6b4

Change-Id: I4f5b1eec29da19eb35d8bda966bda6352950a2d8