Proper shutdown of ActionMode when selecting roots.

When going to other roots, we refresh the whole directory, which will
also refresh ActionMode. The assertion will fail if there was a previous
selection, and if we didn't do proper shut down beforehand.

Bug: 34771762
Bug: 34712136

Test: New FilesActivityUiTest#testNavigate_whileHasSelection
Change-Id: I3cfe094ccaa5d4f343f91e469791e7d1ebfe792f