Scan for tables without relying upon whereclause

Scan for tables without relying upon whereclause

Fixed bug where an UPDATE statement against a JOIN using MySQL multi-table
format would fail to include the table prefix for the target table if the
statement had no WHERE clause, as only the WHERE clause were scanned to
detect a "multi table update" at that particular point.  The target
is now also scanned if it's a JOIN to get the leftmost table as the
primary table and the additional entries as additional FROM entries.

Fixes: #5617
Change-Id: I26d74afebe06e28af28acf960258f170a1627823