avcodec/utils: Display pixel format information as none ... if unknown instead of omitting it

This is similar to 20a5956b

The difference this change makes affects only rather few files
but looks like:
Stream #0:1: Video: mjpeg, 90k tbr, 90k tbn, 90k tbc
vs.
Stream #0:1: Video: mjpeg, none(bt470bg/unknown/unknown), 90k tbr, 90k tbn, 90k tbc
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/utils.c

@@ -3005,7 +3005,7 @@ void avcodec_string(char *buf, int buf_size, AVCodecContext *enc, int encode)
 
     switch (enc->codec_type) {
     case AVMEDIA_TYPE_VIDEO:
-        if (enc->pix_fmt != AV_PIX_FMT_NONE) {
+        {
             char detail[256] = "(";
 
             av_strlcat(buf, separator, buf_size);
@@ -3013,7 +3013,7 @@ void avcodec_string(char *buf, int buf_size, AVCodecContext *enc, int encode)
             snprintf(buf + strlen(buf), buf_size - strlen(buf),
                  "%s", enc->pix_fmt == AV_PIX_FMT_NONE ? "none" :
                      av_get_pix_fmt_name(enc->pix_fmt));
-            if (enc->bits_per_raw_sample &&
+            if (enc->bits_per_raw_sample && enc->pix_fmt != AV_PIX_FMT_NONE &&
                 enc->bits_per_raw_sample <= av_pix_fmt_desc_get(enc->pix_fmt)->comp[0].depth_minus1)
                 av_strlcatf(detail, sizeof(detail), "%d bpc, ", enc->bits_per_raw_sample);
             if (enc->color_range != AVCOL_RANGE_UNSPECIFIED)