perf dso: Fix use before NULL check introduced by map__dso() introduction

James Clark noticed that the recent 63df0e4b ("perf map: Add
accessor for dso") patch accessed map->dso before the 'map' variable was
NULL checked, which is a change in logic that leads to segmentation
faults, so comb thru that patch to fix similar cases.

Fixes: 63df0e4b

 ("perf map: Add accessor for dso")
Acked-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Garry <john.g.garry@oracle.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org
Cc: Suzuki Poulouse <suzuki.poulose@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/lkml/ZD68RYCVT8hqPuxr@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>