MSan may incorrectly report buffer overflow due to undefined behavior

[kcwu]

I cannot recall the exact case confusing MSan. Something like this:

short bar[N];
short foo[len];  // len=0;

MSan may report buffer overflow when access bar.

Build w3m with clang -fsanitize=undefined

case1

00000000: 3c74 6162 6c65 3e30 3c74 643e            <table>0<td>

$ w3m.ubsan -T text/html -dump case1
table.c:1222:18: runtime error: variable length array bound evaluates to non-positive value 0

case2

00000000: 3c74 6162 6c65 3e                        <table>

$ w3m.ubsan -T text/html -dump case2
table.c:1574:20: runtime error: variable length array bound evaluates to non-positive value 0

I don't know they are security related or not. But since MSan may be confused. I think they are worth to fix.

This is found by afl-fuzz.

[kcwu]

Ah, should be MSan, not ASan. I modified the text of description. I will add concrete case later.

[tats]

Fixed with #192