Fix pie control + slim recents issue

Fix slim recents showing without last task (or even empty)

cancelPreloadRecentApps() is called twice when pressing home via pie. (PieView.java, PhoneWindowManager.java)
just block cancelPreloadRecentApps() if home key is pressed via virtual key (pie).

Change-Id: Ife7c9698ada4bf7d069bd32215f415a235cb6a2b