Fix incorrect title in PreferenceActivity.

When navigating from a preference panel back to the headers in single pane,
the title was not restored and the original one (of the previous
preference panel) was kept instead.

Bug: b/35468759
Test: Is covered in ag/1761868
Change-Id: I30cc4c1d2a53d05411cc849ce8423b694c76976a
1 file changed