Bug 37508: Don't return Internal server error when running report

To test:
1 - Create a report like:
SELECT "a"
FROM borrowers
WHERE <<Test>> != ''
2 - Run report
3 - Enter "password"
4 - Internal server error / stacktrace
5 - Apply patch
6 - Repeat
7 - Get a yellow warning box

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>

reports/guided_reports.pl

@@ -846,7 +846,7 @@ elsif ($phase eq 'Run this report'){
             );
             my $total;
             if (!$sth) {
-                die "execute_query failed to return sth for report $report_id: $sql";
+                push @errors, "Report could not be run " . $errors;
             } elsif ( !$errors ) {
                 $total = nb_rows($sql) || 0;
                 my $headers = header_cell_loop($sth);