Merge "launcher: check if task still exists before leaving it in focus" into sc-v2-dev am: 03f0c67420 am: 9ddcedd49a

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/Launcher3/+/15273350

Change-Id: I2ca15b7f9b8c182fe4f2ed49960fe55b923c5ec0