Issue with rigctl_server return value when receiving invalid commands

[WaterBlock623]

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Hardware

• CPU: AMD Ryzen 7 5800H
• RAM: 64GB
• GPU: NVIDIA GeForce RTX 3060 Laptop
• SDR: None

Software

• Operating System: Windows 10 x64
• SDR++: v1.2.1 (Built at 05:11:16, Otc 9 2025)

Bug Description
According to the Hamlib Rigctld documentation, the 'x' in "RPRT x" returned by rigctld upon execution failure should be a negative number.

e.g.

SDRPlusPlus/misc_modules/rigctl_server/src/main.cpp

Lines 391 to 396 in 4658a1a

	// if number of arguments isn't correct, return error
	if (parts.size() != 2) {
	resp = "RPRT 1\n";
	client->write(resp.size(), (uint8_t*)resp.c_str());
	return;
	}

Steps To Reproduce

1. Send any invalid command.