This update for stb fixes the following issues:

Addressing the follow security issues (boo#1216478):

* CVE-2019-13217: heap buffer overflow in start_decoder()
* CVE-2019-13218: stack buffer overflow in compute_codewords()
* CVE-2019-13219: uninitialized memory in vorbis_decode_packet_rest()
* CVE-2019-13220: out-of-range read in draw_line()
* CVE-2019-13221: issue with large 1D codebooks in lookup1_values()
* CVE-2019-13222: unchecked NULL returned by get_window()
* CVE-2019-13223: division by zero in predict_point()