[easy][PTE] Ensure the stream points to the beginning before calling getFileFormat (#75437)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/75437
To avoid potential FileFormatError when geting the format of the input stream, move the pointer to the beg of the stream to read the magic bytes
ghstack-source-id: 153308166
Test Plan: Ci
Reviewed By: iseeyuan
Differential Revision: D35469481
fbshipit-source-id: 489fae30a0fdea5bd7baea486bb0733a88816778
(cherry picked from commit ac87007dd300c7392a2df6dc73a4c2dd003c432b)
