lavfi/showinfo: check plane count before dereferencing.

libavfilter/vf_showinfo.c

@@ -50,7 +50,7 @@ static int filter_frame(AVFilterLink *inlink, AVFilterBufferRef *frame)
     uint32_t plane_checksum[4] = {0}, checksum = 0;
     int i, plane, vsub = desc->log2_chroma_h;
 
-    for (plane = 0; frame->data[plane] && plane < 4; plane++) {
+    for (plane = 0; plane < 4 && frame->data[plane]; plane++) {
         int64_t linesize = av_image_get_linesize(frame->format, frame->video->w, plane);
         uint8_t *data = frame->data[plane];
         int h = plane == 1 || plane == 2 ? inlink->h >> vsub : inlink->h;
@@ -80,7 +80,7 @@ static int filter_frame(AVFilterLink *inlink, AVFilterBufferRef *frame)
            av_get_picture_type_char(frame->video->pict_type),
            checksum, plane_checksum[0]);
 
-    for (plane = 1; frame->data[plane] && plane < 4; plane++)
+    for (plane = 1; plane < 4 && frame->data[plane]; plane++)
         av_log(ctx, AV_LOG_INFO, " %08X", plane_checksum[plane]);
     av_log(ctx, AV_LOG_INFO, "]\n");