stream_out:mosaic_bridge: clean the local es_format_t after it's used

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/stream_out/mosaic_bridge.c

@@ -393,6 +393,7 @@ static sout_stream_id_sys_t * Add( sout_stream_t *p_stream, const es_format_t *p
         if( p_sys->i_chroma )
             fmt.video.i_chroma = p_sys->i_chroma;
         filter_chain_Reset( p_sys->p_vf2, &fmt, &fmt );
+        es_format_Clean( &fmt );
         filter_chain_AppendFromString( p_sys->p_vf2, psz_chain );
         free( psz_chain );
     }