perf hist stdio: Do bounds check when printing callchains to avoid UB with new gcc...

perf hist stdio: Do bounds check when printing callchains to avoid UB with new gcc versions

Do a simple bounds check to avoid this on new gcc versions:

  31    15.81 fedora:rawhide                : FAIL gcc version 15.0.1 20250225 (Red Hat 15.0.1-0) (GCC)
    In function 'callchain__fprintf_left_margin',
        inlined from 'callchain__fprintf_graph.constprop' at ui/stdio/hist.c:246:12:
    ui/stdio/hist.c:27:39: error: iteration 2147483647 invokes undefined behavior [-Werror=aggressive-loop-optimizations]
       27 |         for (i = 0; i < left_margin; i++)
          |                                      ~^~
    ui/stdio/hist.c:27:23: note: within this loop
       27 |         for (i = 0; i < left_margin; i++)
          |                     ~~^~~~~~~~~~~~~
    cc1: all warnings being treated as errors

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Link: https://lore.kernel.org/r/20250310194534.265487-4-acme@kernel.org
Signed-off-by: Namhyung Kim <namhyung@kernel.org>