Very long loop while parsing in MachOFile::parse

[Pastequee]

Hello, while fuzzing I found a binary file (probably ill-formed) that takes around 10 minutes to be parsed on my machine. But the file is only 396 bytes. This might not be a bug and just an expected outcome of the binary lying about its data, but it would be nice if this can be avoided.
What I've discovered if this can help is that this while loop in MachOFile::parse is looping all the time over commands.next()

object/src/read/macho/file.rs

Lines 58 to 69 in a3706b5

	while let Ok(Some(command)) = commands.next() {
	if let Some((segment, section_data)) = Mach::Segment::from_command(command)? {
	let segment_index = segments.len();
	segments.push(MachOSegmentInternal { segment, data });
	for section in segment.sections(endian, section_data)? {
	let index = SectionIndex(sections.len() + 1);
	sections.push(MachOSectionInternal::parse(index, segment_index, section));
	}
	} else if let Some(symtab) = command.symtab()? {
	symbols = symtab.symbols(endian, data)?;
	}
	}

And the next implementation of LoadCommandIterator is decrementing its inner variable ncmds by 1 each iteration and returning None when it's 0. But the thing is the initial value of ncmds is 3 992 977 412 😮

Here is the file to reproduce: test.zip

[philipc]

Thanks very much for the report. That test file also uncovered a couple more bugs, all fixed in #516.