[flexiglass] Fixes extraneous haptic feedback in pattern bouncer.

There's a bug where we vibrate when we first open the bouncer UI in the
pattern configuration and when we stop dragging. This CL fixes that.

Bug: 281871687
Test: manually verified that, after the fix, we only get haptic feedback
when selecting a new dot and not when we first bring up the UI nor when
we stop dragging.

Change-Id: I808698e74a3d9300c11b7422fc70dfdfc5fea80b

packages/SystemUI/compose/features/src/com/android/systemui/bouncer/ui/composable/PatternBouncer.kt

@@ -100,10 +100,14 @@ internal fun PatternBouncer(
 
     // When the current dot is changed, we need to update our animations.
     LaunchedEffect(currentDot, isAnimationEnabled) {
-        view.performHapticFeedback(
-            HapticFeedbackConstants.VIRTUAL_KEY,
-            HapticFeedbackConstants.FLAG_IGNORE_VIEW_SETTING,
-        )
+        // Perform haptic feedback, but only if the current dot is not null, so we don't perform it
+        // when the UI first shows up or when the user lifts their pointer/finger.
+        if (currentDot != null) {
+            view.performHapticFeedback(
+                HapticFeedbackConstants.VIRTUAL_KEY,
+                HapticFeedbackConstants.FLAG_IGNORE_VIEW_SETTING,
+            )
+        }
 
         if (!isAnimationEnabled) {
             return@LaunchedEffect