Implements #170 concurrent encoding

Also resolves some other bug issues.

components/codecs/src/nvpipe_decoder.cpp

@@ -69,6 +69,12 @@ bool NvPipeDecoder::decode(const ftl::codecs::Packet &pkt, cv::cuda::GpuMat &out
 	// No I-Frame yet so don't attempt to decode P-Frames.
 	if (!seen_iframe_) return false;
 
+	// Final checks for validity
+	if (pkt.data.size() == 0 || tmp_.empty()) {
+		LOG(ERROR) << "Failed to decode packet";
+		return false;
+	}
+
 	int rc = NvPipe_Decode(nv_decoder_, pkt.data.data(), pkt.data.size(), tmp_.data, tmp_.cols, tmp_.rows, tmp_.step);
 	if (rc == 0) LOG(ERROR) << "NvPipe decode error: " << NvPipe_GetError(nv_decoder_);