workflow_access doesn't properly restore node_access table when disabled

Enabling workflow access deletes the row in the 'node_access' table where 'nid' is 0 (the default access grants for nodes), and this is not restored when workflow_access is disabled. This causes all subsequently created (and possibly updated) nodes without explicit grants in 'node_access' to be inaccessible to all but user 1.

I'm not familiar enough with the code to produce a patch, but I have been able to consistently reproduce the effect by enabling and disabling the module, finding I can't access new nodes, manually inserting the missing row, checking again, and repeating a number of times.