perf symbols: Check for valid dso before creating map

dso__new() can return NULL. Hence verify dso before creating a new map.
Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Suggested-by: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Anton Arapov <anton@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20120531114656.23691.54223.sendpatchset@srdronam.in.ibm.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/symbol.c

@@ -2817,8 +2817,11 @@ int machine__load_vmlinux_path(struct machine *machine, enum map_type type,
 
 struct map *dso__new_map(const char *name)
 {
+	struct map *map = NULL;
 	struct dso *dso = dso__new(name);
-	struct map *map = map__new2(0, dso, MAP__FUNCTION);
+
+	if (dso)
+		map = map__new2(0, dso, MAP__FUNCTION);
 
 	return map;
 }