Fix crash if Launcher destroyed before AbsSwipeUpHandler invalidated

Test: manually call finish() in onActivityInit(), no crash when
handler is subsequently invalidated (did crash before this change)
Flag: None
Fixes: 295796661

Change-Id: I2dac7ca87bcdb700da2387309d5ad1d2f4ef43d7
diff --git a/quickstep/src/com/android/quickstep/AbsSwipeUpHandler.java b/quickstep/src/com/android/quickstep/AbsSwipeUpHandler.java
index 796840d..67b0d07 100644
--- a/quickstep/src/com/android/quickstep/AbsSwipeUpHandler.java
+++ b/quickstep/src/com/android/quickstep/AbsSwipeUpHandler.java
@@ -194,6 +194,7 @@
                     ActiveGestureLog.INSTANCE.addLog("Launcher destroyed", LAUNCHER_DESTROYED);
                     mRecentsView = null;
                     mActivity = null;
+                    mStateCallback.clearState(STATE_LAUNCHER_PRESENT);
                 }
             };