image: fix block size for decoded picture (fixes #14547)

(cherry picked from commit ba19bb5eadaa42d7f115969ba289910a6ef1a6c8)

modules/demux/image.c

@@ -147,8 +147,7 @@ static block_t *Decode(demux_t *demux,
 
     size_t size = 0;
     for (int i = 0; i < image->i_planes; i++)
-        size += image->p[i].i_visible_pitch *
-                image->p[i].i_visible_lines;
+        size += image->p[i].i_pitch * image->p[i].i_lines;
 
     data = block_Alloc(size);
     if (!data) {