Fix crash when workspace preview arrives later than expected.

If WallpaperPicker is off-screen, and I strongly believe there's other
conditions that are hard to identify, the workspaceSurface SurfaceView
does not have a Display object, and calling further methods will cause
a crash because downstream, a non-null Display is required in order to
obtain the display ID.

Bug: 185019924
Test: Apply 260 wallpapers, verify crash doesn't occur, verify there
are error logs indicating crash would have happened, but was prevented.
(roughly 4 out of these for all 260)
Change-Id: I045f95ed12309900341129887d78908adbee51d5
1 file changed