vod: fix memleak

Port c7690cec to duplicated code
(cherry picked from commit f7ef9010)
Signed-off-by: Pierre Ynard <linkfanel@yahoo.fr>

modules/stream_out/rtp.c

@@ -1242,12 +1242,14 @@ static sout_stream_id_t *Add( sout_stream_t *p_stream, es_format_t *p_fmt )
 
                     if( i_nal_type == 7 )
                     {
+                        free( p_64_sps );
                         p_64_sps = vlc_b64_encode_binary( p_buffer, i_size );
                         /* XXX: nothing ensures that i_size >= 4 ?? */
                         sprintf_hexa( hexa, &p_buffer[1], 3 );
                     }
                     else if( i_nal_type == 8 )
                     {
+                        free( p_64_pps );
                         p_64_pps = vlc_b64_encode_binary( p_buffer, i_size );
                     }
                     i_buffer -= i_size;