perf evsel: Make evsel__env() always return a valid env

perf evsel: Make evsel__env() always return a valid env

It's possible to have an evsel and evsel->evlist populated without
an evsel->evlist->env, when, e.g., cmd_record is in its error path.

Future patches will add support for evsel__open_strerror to be able
to customize error messaging based on perf_env__{arch,cpuid}, so
let's have evsel__env return &perf_env instead of NULL in that case.

Reviewed-by: Kajol Jain <kjain@linux.ibm.com>
Signed-off-by: Kim Phillips <kim.phillips@amd.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Joao Martins <joao.m.martins@oracle.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Robert Richter <robert.richter@amd.com>
Cc: Stephane Eranian <eranian@google.com>
Link: https://lore.kernel.org/r/20211004214114.188477-1-kim.phillips@amd.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>