More weird compiler warnings

serinus' experimental gcc whines about a few places in network.c:

../../../../../pgsql/src/backend/utils/adt/network.c: In function 'inetnot':
../../../../../pgsql/src/backend/utils/adt/network.c:1893:34: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
1893 | pdst[nb] = ~pip[nb];
| ~~~~~~~~~^~~~~~~~~~
../../../../../pgsql/src/include/utils/inet.h:27:23: note: at offset -1 into destination object 'ipaddr' of size 16
27 | unsigned char ipaddr[16]; /* up to 128 bits of address */
| ^~~~~~
../../../../../pgsql/src/include/utils/inet.h:27:23: note: at offset -1 into destination object 'ipaddr' of size 16

The code in question looks like

{
int nb = ip_addrsize(ip);
unsigned char *pip = ip_addr(ip);
unsigned char *pdst = ip_addr(dst);

while (nb-- > 0)
pdst[nb] = ~pip[nb];
}

There's nothing actually wrong with this, but I'm wondering if
we could silence the warning by changing the loop condition to

while (--nb >= 0)

which seems like it might be marginally more readable anyway.

regards, tom lane