perf tools: Allow passing NULL to intlist__find

So that we can work with optional parameters that may not set up an
intlist.

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-e9tmvgdzehqrza11zs0nbg7g@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/intlist.c

@@ -59,9 +59,14 @@ void intlist__remove(struct intlist *ilist, struct int_node *node)
 
 struct int_node *intlist__find(struct intlist *ilist, int i)
 {
-	struct int_node *node = NULL;
-	struct rb_node *rb_node = rblist__find(&ilist->rblist, (void *)((long)i));
+	struct int_node *node;
+	struct rb_node *rb_node;
+
+	if (ilist == NULL)
+		return NULL;
 
+	node = NULL;
+	rb_node = rblist__find(&ilist->rblist, (void *)((long)i));
 	if (rb_node)
 		node = container_of(rb_node, struct int_node, rb_node);