Fix: Add missing EPSS columns for "no CVEs" case

The materialized view result_vt_epss now also has the columns
epss_severity and max_epss_severity in case there are no CVEs present
when the view is created.

This fixes SQL errors resulting from those missing columns.

src/manage_pg.c

@@ -1849,9 +1849,11 @@ create_view_result_vt_epss ()
          "    epss_score,"
          "    epss_percentile,"
          "    epss_cve,"
+         "    epss_severity,"
          "    max_epss_score,"
          "    max_epss_percentile,"
          "    max_epss_cve"
+         "    max_epss_severity,"
          "  FROM nvts);");
 
   sql ("SELECT create_index ('result_vt_epss_by_vt_id',"