HTTP error logging fixes

Common/Net/HTTPClient.cpp

@@ -387,6 +387,11 @@ int Client::ReadResponseHeaders(net::Buffer *readbuf, std::vector<std::string> &
 		return -1;
 	}
 
+	if (readbuf->empty()) {
+		ERROR_LOG(Log::HTTP, "Empty HTTP header read buffer :(");
+		return -1;
+	}
+
 	// Grab the first header line that contains the http code.
 
 	std::string line;

Common/Net/NetBuffer.cpp

@@ -46,7 +46,7 @@ bool Buffer::FlushSocket(uintptr_t sock, double timeout, bool *cancelled) {
 			int sent = send(sock, &data[pos], end - pos, MSG_NOSIGNAL);
 			// TODO: Do we need some retry logic here, instead of just giving up?
 			if (sent < 0) {
-				ERROR_LOG(Log::IO, "FlushSocket failed to send: %d", errno);
+				ERROR_LOG(Log::IO, "FlushSocket failed to send: errno=%d", errno);
 				return false;
 			}
 			pos += sent;