Fix a possible format overflow in dump_genid()

[ppisar]

GCC 14 called with CFLAGS='-O2 -Wformat-overflow' complains:

/tmp/libsolv/ext/testcase.c: In function ‘dump_genid’:
/tmp/libsolv/ext/testcase.c:1275:33: warning: ‘: genid ’ directive writing 8 bytes into a region of size between 3 and 12 [-Wformat-overflow=]
 1275 |       sprintf(cntbuf, "genid %2d: genid ", cnt++);
  |                                 ^~~~~~~~
/tmp/libsolv/ext/testcase.c:1275:7: note: ‘sprintf’ output between 17 and 26 bytes into a destination of size 20
 1275 |       sprintf(cntbuf, "genid %2d: genid ", cnt++);
  |       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/libsolv/ext/testcase.c:1270:33: warning: ‘: genid ’ directive writing 8 bytes into a region of size between 3 and 12 [-Wformat-overflow=]
 1270 |       sprintf(cntbuf, "genid %2d: genid ", cnt++);
  |                                 ^~~~~~~~
/tmp/libsolv/ext/testcase.c:1270:7: note: ‘sprintf’ output between 17 and 26 bytes into a destination of size 20
 1270 |       sprintf(cntbuf, "genid %2d: genid ", cnt++);
  |       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

That's indeed a bug: sprintf() writes into a 20-byte array cntbuf. cnt is int, 32-bit long integer on x86_64 Linux platform. dump_genid() starts with cnt = 1 and increases. It can go up to 2147483647 decimal value, then wrap to -2147483648 decimal value. That's up to 11 bytes of the integer, plus 14 bytes of a static string, plus 1 byte of a trailing '\0'. 26 bytes in total.

While it's improbable that cnt would amount that long number in real life, it's better to be prepared for the worst. Also a benefit is that static analyzers will be be content.

This patch increases cntbuf[] size to accomodate common 32-bit ints. (Generic, albeit illegible, expression would be:

cntbuf[((sizeof(cnt) * 8 - 1) * 3 / 10 + 1 + 1) + 14 + 1];

but I'm not sure that long expression is worth of it.)

[mlschroe]

Right, thanks for the patch!

[mlschroe]

(dump_genid() is only a debugging aid, so this is not security relevant)