Optimize PcapNg file reader to skip copy of packet comment if not requested. (#2048)

* Skip copy of packet comment string if the user does not request it.

* Fix return.

Author: Dimi1010

Pcap++/header/PcapFileDevice.h

@@ -421,6 +421,9 @@ namespace pcpp
 
 		/// Close the pacp-ng file
 		void close() override;
+
+	private:
+		bool getNextPacketInternal(RawPacket& rawPacket, std::string* packetComment);
 	};
 
 	/// @class PcapNgFileWriterDevice

Pcap++/src/PcapFileDevice.cpp

@@ -817,6 +817,16 @@ namespace pcpp
 	}
 
 	bool PcapNgFileReaderDevice::getNextPacket(RawPacket& rawPacket, std::string& packetComment)
+	{
+		return getNextPacketInternal(rawPacket, &packetComment);
+	}
+
+	bool PcapNgFileReaderDevice::getNextPacket(RawPacket& rawPacket)
+	{
+		return getNextPacketInternal(rawPacket, nullptr);
+	}
+
+	bool PcapNgFileReaderDevice::getNextPacketInternal(RawPacket& rawPacket, std::string* packetComment)
 	{
 		if (m_LightPcapNg == nullptr)
 		{
@@ -857,25 +867,22 @@ namespace pcpp
 			return false;
 		}
 
-		if (pktHeader.comment != nullptr && pktHeader.comment_length > 0)
-		{
-			packetComment = std::string(pktHeader.comment, pktHeader.comment_length);
-		}
-		else
+		if (packetComment != nullptr)
 		{
-			packetComment.clear();
+			if (pktHeader.comment != nullptr && pktHeader.comment_length > 0)
+			{
+				packetComment->assign(pktHeader.comment, pktHeader.comment_length);
+			}
+			else
+			{
+				packetComment->clear();
+			}
 		}
 
 		reportPacketProcessed();
 		return true;
 	}
 
-	bool PcapNgFileReaderDevice::getNextPacket(RawPacket& rawPacket)
-	{
-		std::string temp;
-		return getNextPacket(rawPacket, temp);
-	}
-
 	void PcapNgFileReaderDevice::close()
 	{
 		if (m_LightPcapNg == nullptr)