libstagefright: fix thumbnails for videos with non multiple of 4 width

- videos with width not a multiple of 4 will fail thumbnail
  generation
- this fix changes the dest width in converter routine to the
  rounded up nearest multiple of 4
- this fix will not impact already working videos as they are
  already at the nearest multiple of 4 in width

(cherry picked from commit 18720176cbd6b1817b1396e1c7768ce6f44db910)

Change-Id: I104c2f26706876c5314304508f87a8e35b6d4659
Crs-Fixed: 331371