SetConfigValue: Don't crash when clearing connection user data

Passing NULL to SetConfigValue for k_ESteamNetworkingConfig_ConnectionUserData
at connection scope took the user data special case, which converted the value
with AssignConfigValueTyped() and dereferenced the NULL pointer. The check in
SetConfigValueTyped() that rejects clearing connection user data was never
reached.

Let NULL fall through to SetConfigValueTyped(), so the call fails with "Cannot
clear connection user data" instead of crashing, and add a check for it to the
pipe test.

Author: kwy404

src/steamnetworkingsockets/clientlib/csteamnetworkingsockets.cpp

@@ -2220,8 +2220,9 @@ bool CSteamNetworkingUtils::SetConfigValue( ESteamNetworkingConfigValue eValue,
 		case k_ESteamNetworkingConfig_ConnectionUserData:
 		{
 
-			// We only need special handling when modifying a connection
-			if ( eScopeType != k_ESteamNetworkingConfig_Connection )
+			// We only need special handling when modifying a connection.
+			// Clearing it (NULL) falls through and is rejected by SetConfigValueTyped.
+			if ( eScopeType != k_ESteamNetworkingConfig_Connection || pValue == nullptr )
 				break;
 
 			// Process the user argument, maybe performing type conversion

tests/test_connection.cpp

@@ -1227,6 +1227,9 @@ void Test_pipe()
 		assert( infoBob.m_identityRemote == identAlice );
 	}
 
+	// Connection user data cannot be cleared.  Passing NULL should fail, not crash.
+	assert( !SteamNetworkingUtils()->SetConfigValue( k_ESteamNetworkingConfig_ConnectionUserData, k_ESteamNetworkingConfig_Connection, hAlice, k_ESteamNetworkingConfig_Int64, nullptr ) );
+
 	// Wire up to the global peer state used by TestNetworkConditions / PumpCallbacksAndMakeSureStillConnected.
 	g_peerClient.Reset();
 	g_peerServer.Reset();