Fix asan.test_proc_self_fd (#13540)

Author: kripken

tests/fs/test_proc_self_fd.c

@@ -22,6 +22,7 @@ int main(int argc, char* argv[]) {
   char buf[1024];
   ssize_t s = readlink("/proc/self/fd/0", buf, 1024);
   assert(s > 0);
+  buf[s] = 0;
   printf("fd0: %s\n", buf);
 
   printf("done\n");