Problem:

During ALTER, when filling stored column info, wrong column number is used.
This is because we ignored virtual column when iterating over columns in
table and lead to debug assertion.

Fix:

In InnoDB table cache object, vcols are on stored on one list, stored and
normal columns are stored in another list.
When looking for stored column, ignore the virtual columns to get the right
column number of stored column.

Reviewed by: Thiru <thirunarayanan.balathandayuth@oracle.com>,
             Satya <satya.bodapati@oracle.com>
RB: 17939