XBM: Fix signed integer overflow.

Parsing an XBM file with pixel bits larger than int leads to undefined
behavior (signed integer overflow).

Since only the lowest 8 bits are used, this patched code produces the
same images as before.

Also do not increment gotone but set it to a value. If more than
INT_MAX values are parsed, this int would overflow as well.

Proof of Concept (compile with -fsanitize=undefined or -ftrapv):

static unsigned char poc_bits[] = {
0xFFFFFFFF };

0 files changed, 0 insertions, 0 deletions