MDL-41359 database: no table columns is a dml_excpeiton

When insert_record is called and it doesn't find any columns
to insert data into, that is a dml_exception as you need at least
one column in the database to insert into it.  This can happen
when you have created a zero column database table, or the table
does not exist.

lib/dml/pgsql_native_moodle_database.php

@@ -876,6 +876,10 @@ class pgsql_native_moodle_database extends moodle_database {
         $dataobject = (array)$dataobject;
 
         $columns = $this->get_columns($table);
+        if (empty($columns)) {
+            throw new dml_exception('ddltablenotexist', $table);
+        }
+
         $cleaned = array();
         $blobs   = array();