git-apply doesn't work in VFS4G if files are not hydrated

Copied from 924426 in the old Azure Repos backlog.

Steps to reproduce:

1. Build a patch off any commit. Easiest way is to checkout a new branch off master in GVFS and make a change in a file, (e.g. Readme.md) then commit that change to a new branch. Generate the patch by running:
   git format-patch master --stdout > test.patch
2. Clone a new enlistment of the GVFS repo to make sure all files are unhydrated.
3. Apply the patch generated in (1) by running: git apply test.patch

Expected Behavior:

1. The change to Readme.md is applied

Actual Behavior:
Git complains with "error: Readme.md: No such file or directory"

Note that using the --cached option for apply doesn't fix the problem since it does put the modifications in the index but then leaves the working directory with the previous file versions as unstaged changes. The patch will be successfully applied if you commit the changes in the index and then do a reset --hard.

Reproduce the issue in a fresh VFS4G/GVFS enlistment using the described branch, Readme.md change, test.patch, and git apply test.patch steps. Start by tracing how git apply handles an unhydrated Readme.md, then verify that applying the patch updates both the working directory and index without requiring a hard reset.