Check the return value from lua_open()

It always fails when running under valgrind because valgrind does not
implement mmap functionality that LuaJIT requires.

automation/tests/aegisub.cpp

@@ -46,7 +46,12 @@ int main(int argc, char **argv) {
 
 	// Init lua state
 	lua_State *L = lua_open();
-	agi::lua::preload_modules(L);
+	if (!L) {
+		fprintf(stderr, "Failed to create Lua state\n");
+		return 1;
+	}
+
+	preload_modules(L);
 	Install(L, {"include"});
 
 	// Build arg table for scripts

src/auto4_lua.cpp

@@ -401,6 +401,7 @@ namespace {
 
 		// create lua environment
 		L = lua_open();
+		if (!L) return;
 
 		bool loaded = false;
 		BOOST_SCOPE_EXIT_ALL(&) { if (!loaded) Destroy(); };