perf map: Fix potential NULL pointer dereference found by smatch tool

Based on the following report from Smatch, fix the potential NULL
pointer dereference check.

  tools/perf/util/map.c:479
  map__fprintf_srccode() error: we previously assumed 'state' could be
  null (see line 466)

  tools/perf/util/map.c
  465         /* Avoid redundant printing */
  466         if (state &&
  467             state->srcfile &&
  468             !strcmp(state->srcfile, srcfile) &&
  469             state->line == line) {
  470                 free(srcfile);
  471                 return 0;
  472         }
  473
  474         srccode = find_sourceline(srcfile, line, &len);
  475         if (!srccode)
  476                 goto out_free_line;
  477
  478         ret = fprintf(fp, "|%-8d %.*s", line, len, srccode);
  479         state->srcfile = srcfile;
              ^^^^^^^
  480         state->line = line;
              ^^^^^^^

This patch validates 'state' pointer before access its elements.

Signed-off-by: Leo Yan <leo.yan@linaro.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alexey Budankov <alexey.budankov@linux.intel.com>
Cc: Alexios Zavras <alexios.zavras@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Changbin Du <changbin.du@intel.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Eric Saint-Etienne <eric.saint.etienne@oracle.com>
Cc: Jin Yao <yao.jin@linux.intel.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Song Liu <songliubraving@fb.com>
Cc: Suzuki Poulouse <suzuki.poulose@arm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Cc: linux-arm-kernel@lists.infradead.org
Fixes: dd2e18e ("perf tools: Support 'srccode' output")
Link: http://lkml.kernel.org/r/20190702103420.27540-8-leo.yan@linaro.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/map.c

@@ -476,8 +476,11 @@ int map__fprintf_srccode(struct map *map, u64 addr,
 		goto out_free_line;
 
 	ret = fprintf(fp, "|%-8d %.*s", line, len, srccode);
-	state->srcfile = srcfile;
-	state->line = line;
+
+	if (state) {
+		state->srcfile = srcfile;
+		state->line = line;
+	}
 	return ret;
 
 out_free_line: