vf_interlace: use image width rather than linesize

Based on a patch by Michael Niedermayer <michaelni@gmx.at>.

libavfilter/vf_interlace.c

@@ -131,16 +131,17 @@ static void copy_picture_field(InterlaceContext *s,
                                int lowpass)
 {
     const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(inlink->format);
+    int hsub = desc->log2_chroma_w;
     int vsub = desc->log2_chroma_h;
     int plane, j;
 
     for (plane = 0; plane < desc->nb_components; plane++) {
+        int cols  = (plane == 1 || plane == 2) ? -(-inlink->w) >> hsub : inlink->w;
         int lines = (plane == 1 || plane == 2) ? -(-inlink->h) >> vsub : inlink->h;
-        ptrdiff_t linesize = av_image_get_linesize(inlink->format, inlink->w, plane);
         uint8_t *dstp = dst_frame->data[plane];
         const uint8_t *srcp = src_frame->data[plane];
 
-        av_assert0(linesize >= 0);
+        av_assert0(cols >= 0);
 
         lines = (lines + (field_type == FIELD_UPPER)) / 2;
         if (field_type == FIELD_LOWER)
@@ -157,14 +158,14 @@ static void copy_picture_field(InterlaceContext *s,
                     srcp_above = srcp; // there is no line above
                 if (j == 1)
                     srcp_below = srcp; // there is no line below
-                s->lowpass_line(dstp, linesize, srcp, srcp_above, srcp_below);
+                s->lowpass_line(dstp, cols, srcp, srcp_above, srcp_below);
                 dstp += dstp_linesize;
                 srcp += srcp_linesize;
             }
         } else {
             av_image_copy_plane(dstp, dst_frame->linesize[plane] * 2,
                                 srcp, src_frame->linesize[plane] * 2,
-                                linesize, lines);
+                                cols, lines);
         }
     }
 }