We use the condition from CHECK OPTION twice handling UPDATE command.
First we construnct 'update_cond' AND 'option_cond'
condition to select records to be updated, then we check the
'option_cond' for the updated row.
The problem is that first 'AND' condition is optimized during the 'select'
which can break 'option_cond' structure, so it will be unusable for
the sectond use - to check the updated row.
Possible soultion is either use copy of the condition in the first
use or to make optimization less traumatic for the operands.
I picked the first one.