reset UploadFile seek after reading

[murrple-1]

Fixes #472

[aminalaee]

Hey, thanks for taking a look.
I think I already handled this in another step:
https://github.com/aminalaee/sqlalchemy-fields/blob/c7147d2cd61efbfe96fc34d615f54f3dc6087de7/sqlalchemy_fields/storages/filesystem.py#L57

But in your use-case you want to load the upload file before saving, which also shouldn't fail.
Can you please update this test: test_create_form_post
to assert user.file.open().read() == b"abc" to make sure nothing is changed.

[murrple-1]

Sorry, I've done my best searching in the repo, and I can't find a test with that name. Which file?

Edit: nvm, found it

[aminalaee]

Thanks for the PR 🎉