Complete widget drop without extra screen animation

When calling Workspace.removeExtraEmptyScreenDelayed() and
Launcher.isWorkspaceLoading is true, the onComplete runnable will
not be called which will prevent the widget from being added to
the workspace.

Change-Id: I753488e7f389a86edf056f934021634391a8fb84
(cherry picked from commit 5b4a0806)