Adjust wallpaper-restore acceptance criteria

Previously the dimension check had implicit orientation sensitivity.
We now make sure to compare the candidate image's width to the smallest
screen dimension for acceptance purposes; this fixes cases when we would
e.g. get a restored image of (1680x2560) but believe that we needed it
to have a max width of 2048, even though it had originated on that same
device -- due to current-orientation issues.

Bug 18448052

Change-Id: I64ca6a4ed91ce1ccc04f5a9a6851e5cfe511b7c7