Fix crash when a layer is destroyed immediately after creation

If a layer handle is destroyed before we commit any transactions, we
will  not be able to promote the legacy layer object in the main thread. This
is a few of the remaining warts with the legacy frontend which we can fixed
once we remove the flag. For now, fix this by checking if the layer was
destroyed before accessing the legacy layer object.

Test: presubmit
Fixes: 318347070
Change-Id: Ia54feb4b483f0981acd198a0af07745cec183863