debug/macho: return FormatError for truncated or empty files

[zheliu2]

When macho.NewFile encounters io.EOF or io.ErrUnexpectedEOF while
reading the Mach-O identifier or file header, wrap the error in a
*FormatError instead of returning the bare error. This allows callers
to reliably use errors.As(err, &formatErr) to distinguish malformed
Mach-O files from actual I/O errors.

Previously, opening an empty or truncated file returned bare io.EOF
or io.ErrUnexpectedEOF, which callers checking for *FormatError
would miss.

This is the debug/macho equivalent of CL 736600 which fixed the same
issue in debug/elf.

Updates #76338

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[gopherbot]

Message from Gopher Robot:

Patch Set 1:

(1 comment)

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