perf sort: Check for SRCLINE_UNKNOWN case in "srcfile" processing

Handle the SRCLINE_UNKNOWN case correctly when processing "srcfile".

Commiter note:

We can't just free it, as it was't allocated via malloc, its a guard
variable.

Reported-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/20150811133655.GC4524@tassilo.jf.intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/sort.c

@@ -330,6 +330,8 @@ static char *get_srcfile(struct hist_entry *e)
 
 	sf = get_srcline(map->dso, map__rip_2objdump(map, e->ip),
 			 e->ms.sym, true);
+	if (!strcmp(sf, SRCLINE_UNKNOWN))
+		return no_srcfile;
 	p = strchr(sf, ':');
 	if (p && *sf) {
 		*p = 0;