parse-events: Let pevent_free() take a NULL pointer

The pevent_free() should ack like other free()s and allow a
NULL pointer to be passed to it which makes error handling a bit
easier for the users of pevent_free().

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Arun Sharma <asharma@fb.com>
Cc: Namhyung Kim <namhyung.kim@lge.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

tools/lib/traceevent/event-parse.c

@@ -4960,13 +4960,20 @@ static void free_event(struct event_format *event)
  */
 void pevent_free(struct pevent *pevent)
 {
-	struct cmdline_list *cmdlist = pevent->cmdlist, *cmdnext;
-	struct func_list *funclist = pevent->funclist, *funcnext;
-	struct printk_list *printklist = pevent->printklist, *printknext;
+	struct cmdline_list *cmdlist, *cmdnext;
+	struct func_list *funclist, *funcnext;
+	struct printk_list *printklist, *printknext;
 	struct pevent_function_handler *func_handler;
 	struct event_handler *handle;
 	int i;
 
+	if (!pevent)
+		return;
+
+	cmdlist = pevent->cmdlist;
+	funclist = pevent->funclist;
+	printklist = pevent->printklist;
+
 	pevent->ref_count--;
 	if (pevent->ref_count)
 		return;