Fix regression in AbsListView CHOICE_MODE_SINGLE

Earlier patch reversed a few lines of code that allowed deselection of
the currently selected item in CHOICE_MODE_SINGLE. Put it back the way
it was.

Bug 7289436

Change-Id: Ia1c5f3238d2faa3dd79e474851333fda90978d3c

Author: adamp

core/java/android/widget/AbsListView.java

@@ -1077,8 +1077,8 @@ public boolean performItemClick(View view, int position, long id) {
                 checkedStateChanged = true;
             } else if (mChoiceMode == CHOICE_MODE_SINGLE) {
                 boolean checked = !mCheckStates.get(position, false);
-                mCheckStates.clear();
                 if (checked) {
+                    mCheckStates.clear();
                     mCheckStates.put(position, true);
                     if (mCheckedIdStates != null && mAdapter.hasStableIds()) {
                         mCheckedIdStates.clear();