Upgrade error null value in column "numcolumns" violates not-null constraint

We recently removed the numcolumns column from views as it is obsolete

But we get an error when upgrading from older versions of Mahara, eg 15.04 as the upgrade script wants to create a new view before the numcolumns column is removed form db but doesn't have a default value for it in lib/view.php

For example, we get this error:

Failed to get a recordset: postgres8 error: [-1: ERROR: null value in column "numcolumns" violates not-null constraint]

From calling the function install_system_portfolio_view() at htdocs/lib/db/upgrade.php line 4182

I'll add back in the default value for numcolumns into the lib/view.php file so that things will save correctly before the column is removed from db during upgrade.