debug/elf: return FormatError on UnexpectedEOF

[MusicalNinjaDad]

Return a FormatError if io.EOF is unexpectedly encountered
while parsing an ELF.

The resulting error will be identified as io.ErrUnexpectedEOF
by errors.Is

Fixes #76338

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[gopherbot]

Message from Keith Randall:

Patch Set 1:

(1 comment)

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[gopherbot]

Message from Mike Foster:

Patch Set 1:

(2 comments)

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[gopherbot]

Message from Mike Foster:

Patch Set 1:

(1 comment)

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[gopherbot]

Message from Mike Foster:

Patch Set 1:

(1 comment)

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