perf stat: Avoid buffer overflow to the aggregation map

perf stat: Avoid buffer overflow to the aggregation map

CPUs may be created and passed to perf_stat__get_aggr (via
config->aggr_get_id), such as in the stat display
should_skip_zero_counter. There may be no such aggr_id, for example,
if running with a thread. Add a missing bound check and just create
IDs for these cases.

Reviewed-by: Thomas Falcon <thomas.falcon@intel.com>
Signed-off-by: Ian Rogers <irogers@google.com>
Tested-by: James Clark <james.clark@linaro.org>
Link: https://lore.kernel.org/r/20250719030517.1990983-3-irogers@google.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>