utils: Null dereference amend

issue namhyung#1553 related Null dereference amend works.

Signed-off-by: Paran Lee <p4ranlee@gmail.com>

cmds/dump.c

@@ -733,6 +733,9 @@ static void dump_raw_kernel_event(struct uftrace_dump_ops *ops,
 	int size = 0;
 
 	event = pevent_find_event(kernel->pevent, frs->addr);
+	if (!event)
+		return;
+
 	event_data = read_kernel_event(kernel, cpu, &size);
 
 	pr_time(frs->time);

utils/kernel.c

@@ -127,6 +127,9 @@ bool check_kernel_pid_filter(void)
 	bool ret = true;
 	char *filename = get_tracing_file("options/function-fork");
 
+	if (filename == NULL)
+		return false;
+
 	if (!access(filename, F_OK))
 		ret = false;
 

utils/script.c

@@ -41,6 +41,9 @@ enum script_type_t get_script_type(const char *str)
 {
 	char *ext = strrchr(str, '.');
 
+	if (ext == NULL)
+		return SCRIPT_UNKNOWN;
+
 	/*
 	 * The given script will be detected by the file suffix.
 	 * As of now, it only handles ".py" suffix for python.