Return 0 for process gpu mem if no entry found am: a7162686b3 am: 3fe4cfd8d3 am: c4dde45c98

Original change: https://android-review.googlesource.com/c/platform/system/memory/libmeminfo/+/1908514

Change-Id: I5033549f94795fd55c83e22a57c413373c8cce7d