Merge branch 'jc/diff-populate-filespec-size-only-fix' into maint

Merge branch 'jc/diff-populate-filespec-size-only-fix' into maint

"git diff --quiet" relies on the size field in diff_filespec to be
correctly populated, but diff_populate_filespec() helper function
made an incorrect short-cut when asked only to populate the size
field for paths that need to go through convert_to_git() (e.g. CRLF
conversion).

* jc/diff-populate-filespec-size-only-fix:
  diff: do not short-cut CHECK_SIZE_ONLY check in diff_populate_filespec()