ftp PORT: don't hang if bind() fails

When the user requests PORT with a specific port or port range, the code
could lock up in an endless loop. There's now an extra conditional that
makes sure to special treat the error and try the local address only
once so a second failure will abort the loop correctly.

Bug: http://curl.haxx.se/bug/view.cgi?id=3433968
Reported by: Gokhan Sengun

lib/ftp.c

@@ -753,6 +753,7 @@ static CURLcode ftp_state_use_port(struct connectdata *conn,
   unsigned short port_min = 0;
   unsigned short port_max = 0;
   unsigned short port;
+  bool possibly_non_local = TRUE;
 
   char *addr = NULL;
 
@@ -869,6 +870,7 @@ static CURLcode ftp_state_use_port(struct connectdata *conn,
       break;
     }
     host = hbuf; /* use this host name */
+    possibly_non_local = FALSE; /* we know it is local now */
   }
 
   /* resolv ip/host to ip */
@@ -932,12 +934,12 @@ static CURLcode ftp_state_use_port(struct connectdata *conn,
     if(bind(portsock, sa, sslen) ) {
       /* It failed. */
       error = SOCKERRNO;
-      if(error == EADDRNOTAVAIL) {
-
+      if(possibly_non_local && (error == EADDRNOTAVAIL)) {
         /* The requested bind address is not local.  Use the address used for
          * the control connection instead and restart the port loop
          */
-        failf(data, "bind(port=%hu) failed: %s", port,
+
+        infof(data, "bind(port=%hu) on non-local address failed: %s", port,
               Curl_strerror(conn, error) );
 
         sslen = sizeof(ss);
@@ -948,6 +950,7 @@ static CURLcode ftp_state_use_port(struct connectdata *conn,
           return CURLE_FTP_PORT_FAILED;
         }
         port = port_min;
+        possibly_non_local = FALSE; /* don't try this again */
         continue;
       }
       else if(error != EADDRINUSE && error != EACCES) {