The output type of the AV_RL32/AV_RB32 macros was signed int. The resulting overflow broke at least some ASF streams with large timestamps (AV_RL32 used in demux_asf.c timestamp parsing code). Fix by adding a cast to uint32_t. This code comes from FFmpeg, and the matching code in Libav/FFmpeg is still broken (but not used there in most common configurations).