[BUGFIX] Migrate workspaces tries to upgrade non existing tables

The migrate workspaces update wizard task tries to upgrade non
existing tables. Check if table exists before executing the query.

Change-Id: I57855c079a8485537888345b61c9b3f0a17ca492
Resolves: #34246
Releases: 6.2
Reviewed-on: https://review.typo3.org/23796
Reviewed-by: Sascha Egerer
Tested-by: Sascha Egerer
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn