Bounce scan: avoid array overrun (read) by checking index instead

nmap_ftp.cc

@@ -339,7 +339,7 @@ void bounce_scan(Target *target, u16 *portarray, int numports,
           } else {
             error("Your FTP bounce server doesn't allow privileged ports, skipping them.");
             while (i < numports && portarray[i] < 1024) i++;
-            if (!portarray[i]) {
+            if (i >= numports) {
               fatal("And you didn't want to scan any unprivileged ports.  Giving up.");
             }
           }