HLTV crashes when an empty clc_stringcmd message is received

[Splatt581]

A crash will occur if in clc_stringcmd after the message id specify immediately the end of the string (03 00 bytes). But it also works if you send a command that does not have Latin characters, that is, only Unicode is present.

How to reproduce:

1. Connect to HLTV server;
2. Execute the cmd тест in the client console;
3. HLTV server should crash.

Perhaps this bug only works on Windows versions of HLTV.

[Splatt581]

@shawns-valve This vulnerability exists in the latest HLTV build - 10185. To fix this bug you should add a check for the absence of an incoming command in BaseClient::ProcessStringCmd and ProxyClient::ProcessStringCmd:

if (!cmdLine.CountToken()) {
		m_System->DPrintf("WARNING! BaseClient::ProcessStringCmd: invalid command string.\n");
		return false;
	}

The solution is taken from ReHLDS commit: https://github.com/dreamstalker/rehlds/pull/838/files