A little cosmetic to convert_VALUES_to_ANY()

Hi,

While debugging the pull-up sublink codes, I noticed the
convert_VALUES_to_ANY().
The function is to convert "where colX in VALUES(xxx)" into SAOP. It
firstly scans the values_list to
make sure no volatile function is in this list, then it scans this
values_list again to check that it
only includes Const items.

We can merge the two scans into one. This can reduce the time complexity
from 2O(n) to O(n).

Also, add a brace for better/more consistent style in the attached patch.

-- 
Thanks,
Tender Wang