ffmpeg: Fix -vstats when coded_frame is not set

There are several encoders which do not set coded_frame
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

ffmpeg.c

@@ -1182,8 +1182,8 @@ static void do_video_stats(OutputStream *ost, int frame_size)
     enc = ost->enc_ctx;
     if (enc->codec_type == AVMEDIA_TYPE_VIDEO) {
         frame_number = ost->st->nb_frames;
-        fprintf(vstats_file, "frame= %5d q= %2.1f ", frame_number, enc->coded_frame->quality / (float)FF_QP2LAMBDA);
-        if (enc->flags&CODEC_FLAG_PSNR)
+        fprintf(vstats_file, "frame= %5d q= %2.1f ", frame_number, enc->coded_frame ? enc->coded_frame->quality / (float)FF_QP2LAMBDA : 0);
+        if (enc->coded_frame && (enc->flags&CODEC_FLAG_PSNR))
             fprintf(vstats_file, "PSNR= %6.2f ", psnr(enc->coded_frame->error[0] / (enc->width * enc->height * 255.0 * 255.0)));
 
         fprintf(vstats_file,"f_size= %6d ", frame_size);
@@ -1196,7 +1196,7 @@ static void do_video_stats(OutputStream *ost, int frame_size)
         avg_bitrate = (double)(ost->data_size * 8) / ti1 / 1000.0;
         fprintf(vstats_file, "s_size= %8.0fkB time= %0.3f br= %7.1fkbits/s avg_br= %7.1fkbits/s ",
                (double)ost->data_size / 1024, ti1, bitrate, avg_bitrate);
-        fprintf(vstats_file, "type= %c\n", av_get_picture_type_char(enc->coded_frame->pict_type));
+        fprintf(vstats_file, "type= %c\n", enc->coded_frame ? av_get_picture_type_char(enc->coded_frame->pict_type) : 'I');
     }
 }