Allow low resolution wallpaper crop

If launcher sets desired dimensions smaller than display size,
don't expand them to match display.
Wallpaper will be scaled to fill display (ag/4867989).
Old bugs: b/11332853 and b/11606952

Bug: 113651690
Bug: 74517029
Test: Needs launcher that sets desired dimensions lower than display size (eg. new TVLauncher).
Flash & wipe, after first boot /data/system/users/0/wallpaper
and /data/system/users/0/wallpaper_orig should be 1x1px black bitmaps.
CTS WallpaperManagerTest

Change-Id: Ic54c3cc5986c37cef8eefc4be99a951c1f952460