Set parallax offset to be 0.5f for default wallpapers.

This ensures they are centered as they were without any offset.

Bug: 25347076
Change-Id: Id773cd89463d47b350e60878c00e1112e0244414
diff --git a/WallpaperPicker/src/com/android/launcher3/WallpaperPickerActivity.java b/WallpaperPicker/src/com/android/launcher3/WallpaperPickerActivity.java
index b40e4bd..5d41238 100644
--- a/WallpaperPicker/src/com/android/launcher3/WallpaperPickerActivity.java
+++ b/WallpaperPicker/src/com/android/launcher3/WallpaperPickerActivity.java
@@ -309,7 +309,7 @@
 
                 @Override
                 public float getParallaxOffset() {
-                    return 0;
+                    return 0.5f;
                 }
             };
             req.result = new DrawableTileSource(a.getContext(),