ffplay: fix updating external clock after seeking

Now it should work for the timestamp based and the byte based case as well.
Also only update the external clock if the seeking was successful.
Signed-off-by: Marton Balint <cus@passwd.hu>

ffplay.c

@@ -2669,8 +2669,13 @@ static int read_thread(void *arg)
                     packet_queue_flush(&is->videoq);
                     packet_queue_put(&is->videoq, &flush_pkt);
                 }
+                if (is->seek_flags & AVSEEK_FLAG_BYTE) {
+                   //FIXME: use a cleaner way to signal obsolete external clock...
+                   update_external_clock_pts(is, (double)AV_NOPTS_VALUE);
+                } else {
+                   update_external_clock_pts(is, seek_target / (double)AV_TIME_BASE);
+                }
             }
-            update_external_clock_pts(is, (seek_target + ic->start_time) / (double)AV_TIME_BASE);
             is->seek_req = 0;
             eof = 0;
         }