Fix null dereference and buffer overflow

[CreativeNameHUH]

Added null checks for stbi__jpeg pointers in stbi__jpeg_load and stbi__jpeg_test functions.

Added 17th element to stbi__jbias array in function stbi__extend_recive parameter n could be 16 causing a buffer overflow on return k + (stbi__jbias[n] & sgn)

[hermet]

Nobody can't access svace outside of samsung :)

[CreativeNameHUH]

Nobody can't access svace outside of samsung :)

Thank you, I've updated the description and the title :)