Fix a compiler warning

src/common/runtime.cpp

@@ -1010,8 +1010,10 @@ int luax_resume(lua_State *L, int nargs, int* nres)
 #if LUA_VERSION_NUM >= 504
 	return lua_resume(L, nullptr, nargs, nres);
 #elif LUA_VERSION_NUM >= 502
+	LOVE_UNUSED(nres);
 	return lua_resume(L, nullptr, nargs);
 #else
+	LOVE_UNUSED(nres);
 	return lua_resume(L, nargs);
 #endif
 }