tree-wide: explicitly unpoison getdents64() memory

Apparently memory sanitizer doesn't grok getdents64() properly. Let's
address that by explicitly marken memory initialized by getdents64() as
unpoisoned.

src/basic/recurse-dir.c

@@ -60,6 +60,8 @@ int readdir_all(int dir_fd,
                 if (n == 0)
                         break;
 
+                msan_unpoison((uint8_t*) de->buffer + de->buffer_size, n);
+
                 de->buffer_size += n;
 
                 if (de->buffer_size < bs - DIRENT_SIZE_MAX) /* Still room for one more entry, then try to

src/basic/stat-util.c

@@ -103,6 +103,8 @@ int dir_is_empty_at(int dir_fd, const char *path) {
         if (n < 0)
                 return -errno;
 
+        msan_unpoison(&buffer, n);
+
         FOREACH_DIRENT_IN_BUFFER(de, &buffer.de, n)
                 if (!dot_or_dot_dot(de->d_name))
                         return 0;