macosx: add webm the filetypes handled by the bundle
stream_dvd: prevent segmentation fault with some broken files

I have a sample where some final chapters are missing. This was causing a
segmentation fault when trying to fetch chapter times for them.

This makes the code ignore those chapters.
mplayer: m_option: fix clang -Wformat compiler warning

Code was using %d format instead %zd to print size_t data.