Trebuchet: Fix NPE

This change fixes a NPE for the overflow menu. Steps:
1.- A device with no physical menu
2.- Install another launcher (xe Launcher2) (overflow menu is only displayed when Trebuchet runs
outside CM or when multiple launchers exists)
3.- Access AllAppDrawer and tap the overflow menu
4.- Tap again the overflow menu or rotate the screen and tap the overflow menu.
5.- NPE

The overflow menu is not recreated in onCreateOptionsMenu when isWorkspaceLocked(). The change
checks if the user is on the AllAppDrawer and forces the recreation of the menu.

Change-Id: Id68dd1f7b0c09a2f62b5f6d4fbef6f217bf98e82
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>