Avoid to count a non-existing variable in profile controller

Summary:
When uploading a file, if there isn't any upload-related error,
the array $errors didn't exist.

This change fixes the following issue:

Uncaught TypeError: count(): Argument #1 ($value) must be of type
Countable|array, null given
in /var/51-wwwroot/zed/controllers/profile.php:170

Test Plan: Upload a file

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://code.zed.dereckson.be/D21