lavc: set bitrate only if >0

Set the bitrate only if >0. Do not set if neither set explicitly nor by
the codec preset - eg. for APV avg_bpp is intentionally set to 0. The
libopenapv uses CQP by default and setting the bitrate explicitly
disables that.

Note that this setting doesn't do anything important - setting the
AVCodecContext::bitrate to 0 does nothing. This change is avoid displaying
"Setting bitrate to 0.0 bps." message.

Author: MartinPulec

src/video_compress/libavcodec.cpp

@@ -919,7 +919,7 @@ bool set_codec_ctx_params(struct state_video_compress_libav *s, AVPixelFormat pi
                 check_av_opt_set<double, true>(s->codec_ctx->priv_data, "crf",
                                                crf, "CRF");
         } else if (strcmp(s->codec_ctx->codec->name, "libopenh264") != 0) {
-                set_bitrate = true;
+                set_bitrate = bitrate > 0;
         }
         if (set_bitrate || params.requested_bitrate > 0) {
                 s->codec_ctx->bit_rate = bitrate;