BUG/MINOR: lua: check buffers before initializing socket

When a socket is initilized in the body context, a segfaut is generated
because the memory pools are not initilized. This atch check if these
memory pool are initialized.
diff --git a/src/hlua.c b/src/hlua.c
index 3f9b909..8ddc0b6 100644
--- a/src/hlua.c
+++ b/src/hlua.c
@@ -1731,6 +1731,12 @@
 	socket = MAY_LJMP(lua_newuserdata(L, sizeof(*socket)));
 	memset(socket, 0, sizeof(*socket));
 
+	/* Check if the various memory pools are intialized. */
+	if (!pool2_session || !pool2_channel || !pool2_buffer) {
+		hlua_pusherror(L, "socket: uninitialized pools.");
+		goto out_fail_conf;
+	}
+
 	/* Pop a class session metatable and affect it to the userdata. */
 	lua_rawgeti(L, LUA_REGISTRYINDEX, class_socket_ref);
 	lua_setmetatable(L, -2);