Fixes crash calling setSecure on a socket not yet connected.

Calling setSecure on a socket that isn't connected yet causes
a nasty crash. This commit adds a check and issues a Lua error
instead.

fixes #16

Author: ignacio

lib/luanode/net.lua

@@ -392,6 +392,12 @@ end
 
 
 function Socket:setSecure(context)
+
+	-- We need a socket here in order to make it secure
+	if not self._raw_socket then
+		error("Socket is closed.")
+	end
+
 	-- Do we have openssl crypto?
 	local SecureContext = process.SecureContext
 	--local SecureStream = process.SecureStream