perf record: Fix a segfault in record__read_lost_samples()

When it fails to open events record__open() returns without setting the
session->evlist.  Then it gets a segfault in the function trying to read
lost sample counts.  You can easily reproduce it as a normal user like:

  $ perf record -p 1 true
  ...
  perf: Segmentation fault
  ...

Skip the function if it has no evlist.  And add more protection for evsels
which are not properly initialized.

Fixes: a49aa8a54e861af1 ("perf record: Read and inject LOST_SAMPLES events")
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Leo Yan <leo.yan@linaro.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: https://lore.kernel.org/r/20220909235024.278281-1-namhyung@kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>