Provide a default for enabled columns

Due to a race in item instantiation if the process table view is instantiated before the column configuration dialog the enabled attributes will be initially empty. However we still enable columns which then will be filtered out, confusing the proxy model stack as there will be no valid parents anymore because the first column has been filtered out but still claiming to have rows. Delaying assignment of attributes causes a stack overflow due to QSortFilterProxyModelPrivate::recursiveChildAcceptsRows calling itself. Providing here a default enabled column is a straightfoward fix instead of trying to find the exact point of failure in the the proxymodels provided by us and upstream and matches the default for columnDisplay. BUG:470784