cl_dll: environment: Fix MsgFunc_ReceiveW

[GLoOoccK]

MsgFunc_ReceiveW returned early after hitting the validation guard when weather type 0 was sent, preventing the weather state from being cleared.

This validation was originally present in rain.cpp but was lost when the file was removed.

Reference:

cs16-client/cl_dll/rain.cpp

Lines 475 to 479 in 0879a46

	if( iWeatherType == 0 )
	{
	ResetRain();
	return 1;
	}

[GLoOoccK]

cc @a1batross @Vladislav4KZ