Explicitly set mAllowGoingDown = false when only up is allowed

Test: swipe up and down on a task, then scroll to clear all and
try it again; should go up but not down in the second case
Fixes: 187349538

Change-Id: I0879bafb3b5bb3c5ced8a502c98bfba7a3ce8a51

quickstep/src/com/android/launcher3/uioverrides/touchcontrollers/TaskViewTouchController.java

@@ -167,6 +167,7 @@ public abstract class TaskViewTouchController<T extends BaseDraggingActivity>
                                 mAllowGoingDown = true;
                                 directionsToDetectScroll = DIRECTION_BOTH;
                             } else {
+                                mAllowGoingDown = false;
                                 directionsToDetectScroll = upDirection;
                             }
                         }