Show error when can not switch to data view for tables

Summary:
This could happen when someone creates a table with a reserved SQL
keyword, such as “table”: KDb could not create the cursor because it
does not yet support escaping such keywords.

The issue was that KexiDataTableView::setData ignored the return value
of KexiDataScrollArea. Probably because it is a slot, but in this case
it is called as a “regular” function and it is possible to retrieve its
return value.

FIXED-IN:3.2.1

Reviewers: staniek, piggz

Reviewed By: staniek

Subscribers: Kexi-Devel-list

Tags: KEXI

Differential Revision: https://phabricator.kde.org/D29286