patch: correctly parse two-address append in ed-diff

[mknos]

• When processing an append ("a") command in an ed-style diff, line number ranges are not parsed correctly
• If a range (e.g. "1,2") is given as a prefix to "a", the 2nd address ("2") is used as the target address
• Regular diff tools don't output "a" commands with 2 addresses so this is a corner case
• ed-style diffs can be pasted from a previous ed editor session or typed manually, so having extra validation here is helpful
• To test this, I bypassed the code for running an external ed program
• I modified a diff generated by "diff -e", changing the "322a" command to "1,322a"... the file is patched successfully

%cat bad.diffe 
1,322a
	my $Maxlen = 1;		# longest string for current directory
.
317,318d
113d
%perl patch -e ls bad.diffe 
Hmm...  Looks like an ed diff to me...
Patching file ls using Plan A...
Hunk #1 succeeded at 113
Hunk #2 succeeded at 317
Hunk #3 succeeded at 322
done
%cmp ls ls2

[coveralls]

Pull Request Test Coverage Report for Build 13511545565

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 72.349%

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Totals
Change from base Build 13503527620:	0.0%
Covered Lines:	348
Relevant Lines:	481

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💛 - Coveralls

[mknos]

SEE ALSO:
https://lists.gnu.org/archive/html/bug-patch/2025-02/msg00019.html

I submitted this other bug report because GNU patch seemed to fail when processing my test input file with [valid] ed command "1,322a". See how test cases for this project can help the wider Loonix world...

[briandfoy]

changes: handle line range correctly for append operations