ffplay: Continue if the file was appended to.

This is a bit experimental
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

ffplay.c

@@ -2568,6 +2568,7 @@ static int decode_thread(void *arg)
                     goto fail;
                 }
             }
+            eof=0;
             continue;
         }
         ret = av_read_frame(ic, pkt);